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 $182.80   10.519%   $202.0287   $202.03   $202.05   $202.00  
  Purchase #2 $96.59   8.222%   $104.5316   $104.53   $104.55   $104.50  
  Purchase #3 $240.39   8.765%   $261.4602   $261.46   $261.45   $261.50  
  Purchase #4 $56.61   13.471%   $64.2359   $64.24   $64.25   $64.20  
  Purchase #5 $154.29   12.327%   $173.3093   $173.31   $173.30   $173.30  
  Purchase #6 $248.55   6.123%   $263.7687   $263.77   $263.75   $263.80  
  Purchase #7 $77.67   5.443%   $81.8976   $81.90   $81.90   $81.90  
  7 purchase totals = $1,056.90       $1,151.2320   $1,151.24   $1,151.25   $1,151.20