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 $137.69   12.544%   $154.9618   $154.96   $154.95   $155.00  
  Purchase #2 $62.93   12.111%   $70.5515   $70.55   $70.55   $70.60  
  Purchase #3 $172.94   13.216%   $195.7958   $195.80   $195.80   $195.80  
  Purchase #4 $49.96   8.825%   $54.369   $54.37   $54.35   $54.40  
  Purchase #5 $19.39   6.776%   $20.7039   $20.70   $20.70   $20.70  
  Purchase #6 $60.55   7.569%   $65.133   $65.13   $65.15   $65.10  
  Purchase #7 $216.69   11.388%   $241.3667   $241.37   $241.35   $241.40  
  7 purchase totals = $720.15       $802.8817   $802.88   $802.85   $803.00