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 $245.25   3.823%   $254.6259   $254.63   $254.65   $254.60  
  Purchase #2 $195.76   4.829%   $205.2133   $205.21   $205.20   $205.20  
  Purchase #3 $69.92   9.786%   $76.7624   $76.76   $76.75   $76.80  
  Purchase #4 $132.84   3.644%   $137.6807   $137.68   $137.70   $137.70  
  Purchase #5 $149.65   6.538%   $159.4341   $159.43   $159.45   $159.40  
  Purchase #6 $128.79   6.542%   $137.2154   $137.22   $137.20   $137.20  
  Purchase #7 $200.84   12.329%   $225.6016   $225.60   $225.60   $225.60  
  7 purchase totals = $1,123.05       $1,196.5334   $1,196.53   $1,196.55   $1,196.50