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 $141.82   13.460%   $160.909   $160.91   $160.90   $160.90  
  Purchase #2 $56.34   9.692%   $61.8005   $61.80   $61.80   $61.80  
  Purchase #3 $133.77   9.851%   $146.9477   $146.95   $146.95   $146.90  
  Purchase #4 $224.94   4.467%   $234.9881   $234.99   $235.00   $235.00  
  Purchase #5 $228.31   3.311%   $235.8693   $235.87   $235.85   $235.90  
  Purchase #6 $17.66   7.827%   $19.0422   $19.04   $19.05   $19.00  
  Purchase #7 $63.39   5.228%   $66.704   $66.70   $66.70   $66.70  
  7 purchase totals = $866.23       $926.2608   $926.26   $926.25   $926.20