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 $104.83   13.758%   $119.2525   $119.25   $119.25   $119.30  
  Purchase #2 $139.84   4.295%   $145.8461   $145.85   $145.85   $145.80  
  Purchase #3 $33.46   8.525%   $36.3125   $36.31   $36.30   $36.30  
  Purchase #4 $174.46   12.277%   $195.8785   $195.88   $195.90   $195.90  
  Purchase #5 $105.94   10.230%   $116.7777   $116.78   $116.80   $116.80  
  Purchase #6 $194.39   5.230%   $204.5566   $204.56   $204.55   $204.60  
  Purchase #7 $121.85   7.561%   $131.0631   $131.06   $131.05   $131.10  
  7 purchase totals = $874.77       $949.6870   $949.69   $949.70   $949.80