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 $47.28   8.507%   $51.3021   $51.30   $51.30   $51.30  
  Purchase #2 $132.25   9.163%   $144.3681   $144.37   $144.35   $144.40  
  Purchase #3 $77.91   13.284%   $88.2596   $88.26   $88.25   $88.30  
  Purchase #4 $25.62   12.517%   $28.8269   $28.83   $28.85   $28.80  
  Purchase #5 $130.44   10.387%   $143.9888   $143.99   $144.00   $144.00  
  Purchase #6 $146.34   7.812%   $157.7721   $157.77   $157.75   $157.80  
  Purchase #7 $220.80   4.688%   $231.1511   $231.15   $231.15   $231.20  
  7 purchase totals = $780.64       $845.6687   $845.67   $845.65   $845.80