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 $48.68   6.518%   $51.853   $51.85   $51.85   $51.90  
  Purchase #2 $159.29   3.585%   $165.0005   $165.00   $165.00   $165.00  
  Purchase #3 $54.52   13.770%   $62.0274   $62.03   $62.05   $62.00  
  Purchase #4 $217.95   10.676%   $241.2183   $241.22   $241.20   $241.20  
  Purchase #5 $76.57   11.833%   $85.6305   $85.63   $85.65   $85.60  
  Purchase #6 $85.25   3.699%   $88.4034   $88.40   $88.40   $88.40  
  Purchase #7 $194.66   6.245%   $206.8165   $206.82   $206.80   $206.80  
  7 purchase totals = $836.92       $900.9496   $900.95   $900.95   $900.90