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 $58.30   10.358%   $64.3387   $64.34   $64.35   $64.30  
  Purchase #2 $70.69   10.226%   $77.9188   $77.92   $77.90   $77.90  
  Purchase #3 $105.92   4.585%   $110.7764   $110.78   $110.80   $110.80  
  Purchase #4 $51.49   4.145%   $53.6243   $53.62   $53.60   $53.60  
  Purchase #5 $56.79   5.505%   $59.9163   $59.92   $59.90   $59.90  
  Purchase #6 $246.87   7.785%   $266.0888   $266.09   $266.10   $266.10  
  Purchase #7 $218.43   10.610%   $241.6054   $241.61   $241.60   $241.60  
  7 purchase totals = $808.49       $874.2687   $874.28   $874.25   $874.20