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 $162.76   13.180%   $184.2118   $184.21   $184.20   $184.20  
  Purchase #2 $32.97   5.457%   $34.7692   $34.77   $34.75   $34.80  
  Purchase #3 $202.60   11.293%   $225.4796   $225.48   $225.50   $225.50  
  Purchase #4 $197.91   4.728%   $207.2672   $207.27   $207.25   $207.30  
  Purchase #5 $24.41   12.346%   $27.4237   $27.42   $27.40   $27.40  
  Purchase #6 $95.29   9.190%   $104.0472   $104.05   $104.05   $104.00  
  Purchase #7 $165.60   7.648%   $178.2651   $178.27   $178.25   $178.30  
  7 purchase totals = $881.54       $961.4638   $961.47   $961.40   $961.50