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 $84.47   11.605%   $94.2727   $94.27   $94.25   $94.30  
  Purchase #2 $126.45   13.337%   $143.3146   $143.31   $143.30   $143.30  
  Purchase #3 $241.60   6.297%   $256.8136   $256.81   $256.80   $256.80  
  Purchase #4 $86.34   5.474%   $91.0663   $91.07   $91.05   $91.10  
  Purchase #5 $162.62   9.349%   $177.8233   $177.82   $177.80   $177.80  
  Purchase #6 $147.55   11.418%   $164.3973   $164.40   $164.40   $164.40  
  Purchase #7 $26.62   6.131%   $28.2521   $28.25   $28.25   $28.30  
  7 purchase totals = $875.65       $955.9399   $955.93   $955.85   $956.00