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 $73.44   11.158%   $81.6344   $81.63   $81.65   $81.60  
  Purchase #2 $245.32   3.579%   $254.1   $254.10   $254.10   $254.10  
  Purchase #3 $58.39   6.177%   $61.9968   $62.00   $62.00   $62.00  
  Purchase #4 $232.96   5.102%   $244.8456   $244.85   $244.85   $244.80  
  Purchase #5 $62.47   9.348%   $68.3097   $68.31   $68.30   $68.30  
  Purchase #6 $69.72   11.503%   $77.7399   $77.74   $77.75   $77.70  
  Purchase #7 $153.45   7.399%   $164.8038   $164.80   $164.80   $164.80  
  7 purchase totals = $895.75       $953.4302   $953.43   $953.45   $953.30