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 $57.79   4.260%   $60.2519   $60.25   $60.25   $60.30  
  Purchase #2 $19.87   10.184%   $21.8936   $21.89   $21.90   $21.90  
  Purchase #3 $239.82   6.568%   $255.5714   $255.57   $255.55   $255.60  
  Purchase #4 $95.56   12.273%   $107.2881   $107.29   $107.30   $107.30  
  Purchase #5 $112.61   5.506%   $118.8103   $118.81   $118.80   $118.80  
  Purchase #6 $162.73   8.360%   $176.3342   $176.33   $176.35   $176.30  
  Purchase #7 $118.91   13.808%   $135.3291   $135.33   $135.35   $135.30  
  7 purchase totals = $807.29       $875.4786   $875.47   $875.50   $875.50