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 $246.51   7.738%   $265.5849   $265.58   $265.60   $265.60  
  Purchase #2 $206.97   3.107%   $213.4006   $213.40   $213.40   $213.40  
  Purchase #3 $132.69   11.708%   $148.2253   $148.23   $148.25   $148.20  
  Purchase #4 $157.79   10.599%   $174.5142   $174.51   $174.50   $174.50  
  Purchase #5 $35.86   6.568%   $38.2153   $38.22   $38.20   $38.20  
  Purchase #6 $191.28   7.375%   $205.3869   $205.39   $205.40   $205.40  
  Purchase #7 $187.36   7.245%   $200.9342   $200.93   $200.95   $200.90  
  7 purchase totals = $1,158.46       $1,246.2614   $1,246.26   $1,246.30   $1,246.20