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 $51.53   11.731%   $57.575   $57.58   $57.60   $57.60  
  Purchase #2 $241.28   9.842%   $265.0268   $265.03   $265.05   $265.00  
  Purchase #3 $30.95   11.477%   $34.5021   $34.50   $34.50   $34.50  
  Purchase #4 $245.54   11.818%   $274.5579   $274.56   $274.55   $274.60  
  Purchase #5 $67.40   4.721%   $70.582   $70.58   $70.60   $70.60  
  Purchase #6 $161.57   7.732%   $174.0626   $174.06   $174.05   $174.10  
  Purchase #7 $110.60   6.742%   $118.0567   $118.06   $118.05   $118.10  
  7 purchase totals = $908.87       $994.3631   $994.37   $994.40   $994.50