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 $49.94   10.281%   $55.0743   $55.07   $55.05   $55.10  
  Purchase #2 $46.56   11.681%   $51.9987   $52.00   $52.00   $52.00  
  Purchase #3 $142.32   9.237%   $155.4661   $155.47   $155.45   $155.50  
  Purchase #4 $181.44   11.649%   $202.5759   $202.58   $202.60   $202.60  
  Purchase #5 $210.84   11.845%   $235.814   $235.81   $235.80   $235.80  
  Purchase #6 $236.75   5.347%   $249.409   $249.41   $249.40   $249.40  
  Purchase #7 $23.88   8.663%   $25.9487   $25.95   $25.95   $25.90  
  7 purchase totals = $891.73       $976.2867   $976.29   $976.25   $976.30