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 $56.34   6.707%   $60.1187   $60.12   $60.10   $60.10  
  Purchase #2 $119.36   6.185%   $126.7424   $126.74   $126.75   $126.70  
  Purchase #3 $174.85   6.232%   $185.7467   $185.75   $185.75   $185.70  
  Purchase #4 $243.48   5.545%   $256.981   $256.98   $257.00   $257.00  
  Purchase #5 $12.37   11.211%   $13.7568   $13.76   $13.75   $13.80  
  Purchase #6 $102.61   13.168%   $116.1217   $116.12   $116.10   $116.10  
  Purchase #7 $97.58   8.801%   $106.168   $106.17   $106.15   $106.20  
  7 purchase totals = $806.59       $865.6353   $865.64   $865.60   $865.60