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 $32.81   5.472%   $34.6054   $34.61   $34.60   $34.60  
  Purchase #2 $8.81   4.606%   $9.2158   $9.22   $9.20   $9.20  
  Purchase #3 $209.34   6.690%   $223.3448   $223.34   $223.35   $223.30  
  Purchase #4 $197.36   4.385%   $206.0142   $206.01   $206.00   $206.00  
  Purchase #5 $73.59   11.204%   $81.835   $81.84   $81.85   $81.80  
  Purchase #6 $171.70   10.538%   $189.7937   $189.79   $189.80   $189.80  
  Purchase #7 $202.90   7.672%   $218.4665   $218.47   $218.45   $218.50  
  7 purchase totals = $896.51       $963.2754   $963.28   $963.25   $963.20