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 $52.76   9.207%   $57.6176   $57.62   $57.60   $57.60  
  Purchase #2 $33.57   8.831%   $36.5346   $36.53   $36.55   $36.50  
  Purchase #3 $64.75   13.721%   $73.6343   $73.63   $73.65   $73.60  
  Purchase #4 $156.78   6.136%   $166.4   $166.40   $166.40   $166.40  
  Purchase #5 $115.92   12.281%   $130.1561   $130.16   $130.15   $130.20  
  Purchase #6 $243.96   4.147%   $254.077   $254.08   $254.10   $254.10  
  Purchase #7 $93.88   4.127%   $97.7544   $97.75   $97.75   $97.80  
  7 purchase totals = $761.62       $816.1740   $816.17   $816.20   $816.20