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 $24.34   3.761%   $25.2554   $25.26   $25.25   $25.30  
  Purchase #2 $245.55   4.603%   $256.8527   $256.85   $256.85   $256.90  
  Purchase #3 $13.67   5.324%   $14.3978   $14.40   $14.40   $14.40  
  Purchase #4 $199.65   8.188%   $215.9973   $216.00   $216.00   $216.00  
  Purchase #5 $191.25   3.449%   $197.8462   $197.85   $197.85   $197.80  
  Purchase #6 $36.37   6.803%   $38.8443   $38.84   $38.85   $38.80  
  Purchase #7 $248.40   3.353%   $256.7289   $256.73   $256.75   $256.70  
  7 purchase totals = $959.23       $1,005.9226   $1,005.93   $1,005.95   $1,005.90