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 $233.26   7.382%   $250.4793   $250.48   $250.50   $250.50  
  Purchase #2 $181.98   9.803%   $199.8195   $199.82   $199.80   $199.80  
  Purchase #3 $169.64   3.545%   $175.6537   $175.65   $175.65   $175.70  
  Purchase #4 $41.51   9.243%   $45.3468   $45.35   $45.35   $45.30  
  Purchase #5 $233.82   7.190%   $250.6317   $250.63   $250.65   $250.60  
  Purchase #6 $35.63   3.202%   $36.7709   $36.77   $36.75   $36.80  
  Purchase #7 $42.46   11.180%   $47.207   $47.21   $47.20   $47.20  
  7 purchase totals = $938.30       $1,005.9089   $1,005.91   $1,005.90   $1,005.90