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 $61.76   3.290%   $63.7919   $63.79   $63.80   $63.80  
  Purchase #2 $200.53   5.709%   $211.9783   $211.98   $212.00   $212.00  
  Purchase #3 $66.98   12.284%   $75.2078   $75.21   $75.20   $75.20  
  Purchase #4 $82.66   4.302%   $86.216   $86.22   $86.20   $86.20  
  Purchase #5 $53.81   9.395%   $58.8654   $58.87   $58.85   $58.90  
  Purchase #6 $223.53   11.501%   $249.2382   $249.24   $249.25   $249.20  
  Purchase #7 $166.64   9.565%   $182.5791   $182.58   $182.60   $182.60  
  7 purchase totals = $855.91       $927.8767   $927.89   $927.90   $927.90