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 $51.77   9.236%   $56.5515   $56.55   $56.55   $56.60  
  Purchase #2 $228.69   8.251%   $247.5592   $247.56   $247.55   $247.60  
  Purchase #3 $54.58   7.274%   $58.5501   $58.55   $58.55   $58.60  
  Purchase #4 $122.39   7.360%   $131.3979   $131.40   $131.40   $131.40  
  Purchase #5 $234.97   3.440%   $243.053   $243.05   $243.05   $243.10  
  Purchase #6 $211.75   8.554%   $229.8631   $229.86   $229.85   $229.90  
  Purchase #7 $40.94   12.809%   $46.184   $46.18   $46.20   $46.20  
  7 purchase totals = $945.09       $1,013.1588   $1,013.15   $1,013.15   $1,013.40