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 $108.96   7.262%   $116.8727   $116.87   $116.85   $116.90  
  Purchase #2 $59.29   8.290%   $64.2051   $64.21   $64.20   $64.20  
  Purchase #3 $73.39   10.694%   $81.2383   $81.24   $81.25   $81.20  
  Purchase #4 $227.29   7.605%   $244.5754   $244.58   $244.60   $244.60  
  Purchase #5 $186.64   13.353%   $211.562   $211.56   $211.55   $211.60  
  Purchase #6 $14.54   7.694%   $15.6587   $15.66   $15.65   $15.70  
  Purchase #7 $216.93   7.687%   $233.6054   $233.61   $233.60   $233.60  
  7 purchase totals = $887.04       $967.7176   $967.73   $967.70   $967.80