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 $113.82   10.201%   $125.4308   $125.43   $125.45   $125.40  
  Purchase #2 $147.55   12.388%   $165.8285   $165.83   $165.85   $165.80  
  Purchase #3 $81.43   7.777%   $87.7628   $87.76   $87.75   $87.80  
  Purchase #4 $28.86   10.620%   $31.9249   $31.92   $31.90   $31.90  
  Purchase #5 $140.42   13.394%   $159.2279   $159.23   $159.25   $159.20  
  Purchase #6 $209.51   3.320%   $216.4657   $216.47   $216.45   $216.50  
  Purchase #7 $197.84   6.599%   $210.8955   $210.90   $210.90   $210.90  
  7 purchase totals = $919.43       $997.5361   $997.54   $997.55   $997.50