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 $68.76   11.459%   $76.6392   $76.64   $76.65   $76.60  
  Purchase #2 $14.45   6.549%   $15.3963   $15.40   $15.40   $15.40  
  Purchase #3 $210.37   6.397%   $223.8274   $223.83   $223.85   $223.80  
  Purchase #4 $64.65   5.145%   $67.9762   $67.98   $68.00   $68.00  
  Purchase #5 $150.45   10.115%   $165.668   $165.67   $165.65   $165.70  
  Purchase #6 $167.85   13.119%   $189.8702   $189.87   $189.85   $189.90  
  Purchase #7 $66.38   13.867%   $75.5849   $75.58   $75.60   $75.60  
  7 purchase totals = $742.91       $814.9622   $814.97   $815.00   $815.00