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 $218.65   6.152%   $232.1013   $232.10   $232.10   $232.10  
  Purchase #2 $193.89   12.359%   $217.8529   $217.85   $217.85   $217.90  
  Purchase #3 $151.33   9.149%   $165.1752   $165.18   $165.20   $165.20  
  Purchase #4 $154.84   12.486%   $174.1733   $174.17   $174.15   $174.20  
  Purchase #5 $61.40   5.577%   $64.8243   $64.82   $64.80   $64.80  
  Purchase #6 $152.46   11.111%   $169.3998   $169.40   $169.40   $169.40  
  Purchase #7 $171.48   6.415%   $182.4804   $182.48   $182.50   $182.50  
  7 purchase totals = $1,104.05       $1,206.0072   $1,206.00   $1,206.00   $1,206.10