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 $148.71   8.420%   $161.2314   $161.23   $161.25   $161.20  
  Purchase #2 $232.73   10.586%   $257.3668   $257.37   $257.35   $257.40  
  Purchase #3 $135.84   6.332%   $144.4414   $144.44   $144.45   $144.40  
  Purchase #4 $101.84   6.866%   $108.8323   $108.83   $108.85   $108.80  
  Purchase #5 $244.84   6.606%   $261.0141   $261.01   $261.00   $261.00  
  Purchase #6 $81.49   9.162%   $88.9561   $88.96   $88.95   $89.00  
  Purchase #7 $127.70   6.799%   $136.3823   $136.38   $136.40   $136.40  
  7 purchase totals = $1,073.15       $1,158.2244   $1,158.22   $1,158.25   $1,158.20