Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $103.89   10.279%   $114.5689   $114.57   $114.55   $114.60  
  Purchase #2 $195.73   12.433%   $220.0651   $220.07   $220.05   $220.10  
  Purchase #3 $149.77   13.549%   $170.0623   $170.06   $170.05   $170.10  
  Purchase #4 $247.87   7.564%   $266.6189   $266.62   $266.60   $266.60  
  Purchase #5 $168.81   11.108%   $187.5614   $187.56   $187.55   $187.60  
  Purchase #6 $124.89   5.470%   $131.7215   $131.72   $131.70   $131.70  
  Purchase #7 $151.44   5.740%   $160.1327   $160.13   $160.15   $160.10  
  7 purchase totals = $1,142.40       $1,250.7308   $1,250.73   $1,250.65   $1,250.80