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 $60.72   12.323%   $68.2025   $68.20   $68.20   $68.20  
  Purchase #2 $127.85   4.681%   $133.8347   $133.83   $133.85   $133.80  
  Purchase #3 $109.31   9.730%   $119.9459   $119.95   $119.95   $119.90  
  Purchase #4 $207.43   13.640%   $235.7235   $235.72   $235.70   $235.70  
  Purchase #5 $145.39   5.709%   $153.6903   $153.69   $153.70   $153.70  
  Purchase #6 $180.84   6.756%   $193.0576   $193.06   $193.05   $193.10  
  Purchase #7 $61.27   8.171%   $66.2764   $66.28   $66.30   $66.30  
  7 purchase totals = $892.81       $970.7309   $970.73   $970.75   $970.70