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 $54.29   7.873%   $58.5643   $58.56   $58.55   $58.60  
  Purchase #2 $161.50   9.596%   $176.9975   $177.00   $177.00   $177.00  
  Purchase #3 $214.47   12.115%   $240.453   $240.45   $240.45   $240.50  
  Purchase #4 $72.58   13.241%   $82.1903   $82.19   $82.20   $82.20  
  Purchase #5 $140.98   13.160%   $159.533   $159.53   $159.55   $159.50  
  Purchase #6 $25.45   13.660%   $28.9265   $28.93   $28.95   $28.90  
  Purchase #7 $183.26   13.270%   $207.5786   $207.58   $207.60   $207.60  
  7 purchase totals = $852.53       $954.2432   $954.24   $954.30   $954.30