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 $64.59   5.796%   $68.3336   $68.33   $68.35   $68.30  
  Purchase #2 $222.58   7.226%   $238.6636   $238.66   $238.65   $238.70  
  Purchase #3 $16.29   5.224%   $17.141   $17.14   $17.15   $17.10  
  Purchase #4 $241.76   3.269%   $249.6631   $249.66   $249.65   $249.70  
  Purchase #5 $59.51   9.424%   $65.1182   $65.12   $65.10   $65.10  
  Purchase #6 $122.63   13.630%   $139.3445   $139.34   $139.35   $139.30  
  Purchase #7 $23.30   9.673%   $25.5538   $25.55   $25.55   $25.60  
  7 purchase totals = $750.66       $803.8178   $803.80   $803.80   $803.80