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 $62.43   3.863%   $64.8417   $64.84   $64.85   $64.80  
  Purchase #2 $225.93   10.697%   $250.0977   $250.10   $250.10   $250.10  
  Purchase #3 $150.93   8.763%   $164.156   $164.16   $164.15   $164.20  
  Purchase #4 $72.35   9.849%   $79.4758   $79.48   $79.50   $79.50  
  Purchase #5 $226.73   6.648%   $241.803   $241.80   $241.80   $241.80  
  Purchase #6 $191.84   8.619%   $208.3747   $208.37   $208.35   $208.40  
  Purchase #7 $243.96   4.163%   $254.1161   $254.12   $254.10   $254.10  
  7 purchase totals = $1,174.17       $1,262.8650   $1,262.87   $1,262.85   $1,262.90