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 $55.83   6.872%   $59.6666   $59.67   $59.65   $59.70  
  Purchase #2 $29.25   10.862%   $32.4271   $32.43   $32.45   $32.40  
  Purchase #3 $217.64   6.619%   $232.0456   $232.05   $232.05   $232.00  
  Purchase #4 $202.64   10.336%   $223.5849   $223.58   $223.60   $223.60  
  Purchase #5 $124.97   8.244%   $135.2725   $135.27   $135.25   $135.30  
  Purchase #6 $81.66   4.338%   $85.2024   $85.20   $85.20   $85.20  
  Purchase #7 $100.88   12.508%   $113.4981   $113.50   $113.50   $113.50  
  7 purchase totals = $812.87       $881.6972   $881.70   $881.70   $881.70