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 $56.95   9.474%   $62.3454   $62.35   $62.35   $62.30  
  Purchase #2 $192.70   7.858%   $207.8424   $207.84   $207.85   $207.80  
  Purchase #3 $95.74   12.417%   $107.628   $107.63   $107.65   $107.60  
  Purchase #4 $208.34   9.114%   $227.3281   $227.33   $227.35   $227.30  
  Purchase #5 $13.66   12.315%   $15.3422   $15.34   $15.35   $15.30  
  Purchase #6 $131.42   11.836%   $146.9749   $146.97   $146.95   $147.00  
  Purchase #7 $47.85   13.585%   $54.3504   $54.35   $54.35   $54.40  
  7 purchase totals = $746.66       $821.8114   $821.81   $821.85   $821.70