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 $95.81   8.775%   $104.2173   $104.22   $104.20   $104.20  
  Purchase #2 $132.42   6.356%   $140.8366   $140.84   $140.85   $140.80  
  Purchase #3 $150.53   7.859%   $162.3602   $162.36   $162.35   $162.40  
  Purchase #4 $101.27   4.441%   $105.7674   $105.77   $105.75   $105.80  
  Purchase #5 $95.88   6.480%   $102.093   $102.09   $102.10   $102.10  
  Purchase #6 $36.99   4.154%   $38.5266   $38.53   $38.55   $38.50  
  Purchase #7 $73.58   11.209%   $81.8276   $81.83   $81.85   $81.80  
  7 purchase totals = $686.48       $735.6287   $735.64   $735.65   $735.60