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 $212.33   11.611%   $236.9836   $236.98   $237.00   $237.00  
  Purchase #2 $64.97   5.206%   $68.3523   $68.35   $68.35   $68.40  
  Purchase #3 $62.57   7.217%   $67.0857   $67.09   $67.10   $67.10  
  Purchase #4 $237.40   12.823%   $267.8418   $267.84   $267.85   $267.80  
  Purchase #5 $213.44   8.366%   $231.2964   $231.30   $231.30   $231.30  
  Purchase #6 $213.63   7.725%   $230.1329   $230.13   $230.15   $230.10  
  Purchase #7 $81.48   10.143%   $89.7445   $89.74   $89.75   $89.70  
  7 purchase totals = $1,085.82       $1,191.4372   $1,191.43   $1,191.50   $1,191.40