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 $64.38   5.806%   $68.1179   $68.12   $68.10   $68.10  
  Purchase #2 $184.47   9.351%   $201.7198   $201.72   $201.70   $201.70  
  Purchase #3 $129.67   7.750%   $139.7194   $139.72   $139.70   $139.70  
  Purchase #4 $55.67   7.674%   $59.9421   $59.94   $59.95   $59.90  
  Purchase #5 $140.40   9.257%   $153.3968   $153.40   $153.40   $153.40  
  Purchase #6 $185.82   12.385%   $208.8338   $208.83   $208.85   $208.80  
  Purchase #7 $193.66   6.661%   $206.5597   $206.56   $206.55   $206.60  
  7 purchase totals = $954.07       $1,038.2895   $1,038.29   $1,038.25   $1,038.20