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 $167.67   11.220%   $186.4826   $186.48   $186.50   $186.50  
  Purchase #2 $137.39   13.759%   $156.2935   $156.29   $156.30   $156.30  
  Purchase #3 $16.49   7.116%   $17.6634   $17.66   $17.65   $17.70  
  Purchase #4 $62.73   12.565%   $70.612   $70.61   $70.60   $70.60  
  Purchase #5 $202.44   12.645%   $228.0385   $228.04   $228.05   $228.00  
  Purchase #6 $180.40   8.182%   $195.1603   $195.16   $195.15   $195.20  
  Purchase #7 $87.82   6.433%   $93.4695   $93.47   $93.45   $93.50  
  7 purchase totals = $854.94       $947.7198   $947.71   $947.70   $947.80