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 $76.46   9.259%   $83.5394   $83.54   $83.55   $83.50  
  Purchase #2 $208.45   8.269%   $225.6867   $225.69   $225.70   $225.70  
  Purchase #3 $218.99   3.570%   $226.8079   $226.81   $226.80   $226.80  
  Purchase #4 $228.72   4.426%   $238.8431   $238.84   $238.85   $238.80  
  Purchase #5 $207.90   5.232%   $218.7773   $218.78   $218.80   $218.80  
  Purchase #6 $178.81   10.336%   $197.2918   $197.29   $197.30   $197.30  
  Purchase #7 $32.56   12.362%   $36.5851   $36.59   $36.60   $36.60  
  7 purchase totals = $1,151.89       $1,227.5313   $1,227.54   $1,227.60   $1,227.50