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 $11.91   9.618%   $13.0555   $13.06   $13.05   $13.10  
  Purchase #2 $127.28   4.227%   $132.6601   $132.66   $132.65   $132.70  
  Purchase #3 $58.71   5.641%   $62.0218   $62.02   $62.00   $62.00  
  Purchase #4 $66.53   13.244%   $75.3412   $75.34   $75.35   $75.30  
  Purchase #5 $247.88   6.352%   $263.6253   $263.63   $263.65   $263.60  
  Purchase #6 $229.30   7.574%   $246.6672   $246.67   $246.65   $246.70  
  Purchase #7 $64.45   5.434%   $67.9522   $67.95   $67.95   $68.00  
  7 purchase totals = $806.06       $861.3233   $861.33   $861.30   $861.40