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 $247.36   6.274%   $262.8794   $262.88   $262.90   $262.90  
  Purchase #2 $58.30   13.632%   $66.2475   $66.25   $66.25   $66.20  
  Purchase #3 $104.35   3.682%   $108.1922   $108.19   $108.20   $108.20  
  Purchase #4 $227.59   4.800%   $238.5143   $238.51   $238.50   $238.50  
  Purchase #5 $199.32   12.757%   $224.7473   $224.75   $224.75   $224.70  
  Purchase #6 $122.32   12.570%   $137.6956   $137.70   $137.70   $137.70  
  Purchase #7 $114.52   5.761%   $121.1175   $121.12   $121.10   $121.10  
  7 purchase totals = $1,073.76       $1,159.3938   $1,159.40   $1,159.40   $1,159.30