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 $66.28   9.393%   $72.5057   $72.51   $72.50   $72.50  
  Purchase #2 $244.75   4.863%   $256.6522   $256.65   $256.65   $256.70  
  Purchase #3 $149.82   5.351%   $157.8369   $157.84   $157.85   $157.80  
  Purchase #4 $184.81   9.685%   $202.7088   $202.71   $202.70   $202.70  
  Purchase #5 $198.60   5.165%   $208.8577   $208.86   $208.85   $208.90  
  Purchase #6 $163.86   9.857%   $180.0117   $180.01   $180.00   $180.00  
  Purchase #7 $25.87   13.741%   $29.4248   $29.42   $29.40   $29.40  
  7 purchase totals = $1,033.99       $1,107.9978   $1,108.00   $1,107.95   $1,108.00