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 $73.54   4.809%   $77.0765   $77.08   $77.10   $77.10  
  Purchase #2 $171.92   9.793%   $188.7561   $188.76   $188.75   $188.80  
  Purchase #3 $163.31   8.725%   $177.5588   $177.56   $177.55   $177.60  
  Purchase #4 $125.76   9.239%   $137.379   $137.38   $137.40   $137.40  
  Purchase #5 $49.33   10.800%   $54.6576   $54.66   $54.65   $54.70  
  Purchase #6 $235.75   4.365%   $246.0405   $246.04   $246.05   $246.00  
  Purchase #7 $68.65   12.551%   $77.2663   $77.27   $77.25   $77.30  
  7 purchase totals = $888.26       $958.7348   $958.75   $958.75   $958.90