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 $54.66   9.522%   $59.8647   $59.86   $59.85   $59.90  
  Purchase #2 $228.87   9.284%   $250.1183   $250.12   $250.10   $250.10  
  Purchase #3 $243.29   11.868%   $272.1637   $272.16   $272.15   $272.20  
  Purchase #4 $19.57   9.510%   $21.4311   $21.43   $21.45   $21.40  
  Purchase #5 $152.35   7.255%   $163.403   $163.40   $163.40   $163.40  
  Purchase #6 $116.70   7.418%   $125.3568   $125.36   $125.35   $125.40  
  Purchase #7 $47.25   13.763%   $53.753   $53.75   $53.75   $53.80  
  7 purchase totals = $862.69       $946.0906   $946.08   $946.05   $946.20