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 $225.63   13.299%   $255.6365   $255.64   $255.65   $255.60  
  Purchase #2 $236.79   8.341%   $256.5407   $256.54   $256.55   $256.50  
  Purchase #3 $41.64   4.408%   $43.4755   $43.48   $43.50   $43.50  
  Purchase #4 $217.91   9.230%   $238.0231   $238.02   $238.00   $238.00  
  Purchase #5 $170.70   8.162%   $184.6325   $184.63   $184.65   $184.60  
  Purchase #6 $85.95   12.647%   $96.8201   $96.82   $96.80   $96.80  
  Purchase #7 $154.62   11.567%   $172.5049   $172.50   $172.50   $172.50  
  7 purchase totals = $1,133.24       $1,247.6333   $1,247.63   $1,247.65   $1,247.50