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 $216.38   11.611%   $241.5039   $241.50   $241.50   $241.50  
  Purchase #2 $121.75   3.779%   $126.3509   $126.35   $126.35   $126.40  
  Purchase #3 $18.43   3.361%   $19.0494   $19.05   $19.05   $19.00  
  Purchase #4 $74.36   7.339%   $79.8173   $79.82   $79.80   $79.80  
  Purchase #5 $10.93   7.691%   $11.7706   $11.77   $11.75   $11.80  
  Purchase #6 $183.51   5.366%   $193.3571   $193.36   $193.35   $193.40  
  Purchase #7 $154.53   11.452%   $172.2268   $172.23   $172.25   $172.20  
  7 purchase totals = $779.89       $844.0760   $844.08   $844.05   $844.10