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 $68.92   7.786%   $74.2861   $74.29   $74.30   $74.30  
  Purchase #2 $234.55   11.638%   $261.8469   $261.85   $261.85   $261.80  
  Purchase #3 $124.65   12.439%   $140.1552   $140.16   $140.15   $140.20  
  Purchase #4 $119.93   10.501%   $132.5238   $132.52   $132.50   $132.50  
  Purchase #5 $219.36   4.292%   $228.7749   $228.77   $228.75   $228.80  
  Purchase #6 $182.94   9.789%   $200.848   $200.85   $200.85   $200.80  
  Purchase #7 $204.99   9.505%   $224.4743   $224.47   $224.45   $224.50  
  7 purchase totals = $1,155.34       $1,262.9092   $1,262.91   $1,262.85   $1,262.90