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 $54.31   11.609%   $60.6148   $60.61   $60.60   $60.60  
  Purchase #2 $250.72   11.793%   $280.2874   $280.29   $280.30   $280.30  
  Purchase #3 $22.34   6.829%   $23.8656   $23.87   $23.85   $23.90  
  Purchase #4 $161.99   7.582%   $174.2721   $174.27   $174.25   $174.30  
  Purchase #5 $104.65   3.604%   $108.4216   $108.42   $108.40   $108.40  
  Purchase #6 $152.84   6.819%   $163.2622   $163.26   $163.25   $163.30  
  Purchase #7 $137.34   13.583%   $155.9949   $155.99   $156.00   $156.00  
  7 purchase totals = $884.19       $966.7186   $966.71   $966.65   $966.80