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 $172.82   13.182%   $195.6011   $195.60   $195.60   $195.60  
  Purchase #2 $148.25   9.299%   $162.0358   $162.04   $162.05   $162.00  
  Purchase #3 $74.57   13.290%   $84.4804   $84.48   $84.50   $84.50  
  Purchase #4 $134.72   11.798%   $150.6143   $150.61   $150.60   $150.60  
  Purchase #5 $188.88   8.471%   $204.88   $204.88   $204.90   $204.90  
  Purchase #6 $148.51   6.413%   $158.0339   $158.03   $158.05   $158.00  
  Purchase #7 $81.80   4.817%   $85.7403   $85.74   $85.75   $85.70  
  7 purchase totals = $949.55       $1,041.3858   $1,041.38   $1,041.45   $1,041.30