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 $60.52   9.573%   $66.3136   $66.31   $66.30   $66.30  
  Purchase #2 $198.64   5.457%   $209.4798   $209.48   $209.50   $209.50  
  Purchase #3 $111.46   8.368%   $120.787   $120.79   $120.80   $120.80  
  Purchase #4 $86.66   12.843%   $97.7897   $97.79   $97.80   $97.80  
  Purchase #5 $129.40   10.411%   $142.8718   $142.87   $142.85   $142.90  
  Purchase #6 $68.82   6.844%   $73.53   $73.53   $73.55   $73.50  
  Purchase #7 $45.91   4.606%   $48.0246   $48.02   $48.00   $48.00  
  7 purchase totals = $701.41       $758.7965   $758.79   $758.80   $758.80