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 $83.78   12.439%   $94.2014   $94.20   $94.20   $94.20  
  Purchase #2 $250.91   4.518%   $262.2461   $262.25   $262.25   $262.20  
  Purchase #3 $144.39   5.719%   $152.6477   $152.65   $152.65   $152.60  
  Purchase #4 $23.30   8.511%   $25.2831   $25.28   $25.30   $25.30  
  Purchase #5 $23.41   8.285%   $25.3495   $25.35   $25.35   $25.30  
  Purchase #6 $162.56   13.652%   $184.7527   $184.75   $184.75   $184.80  
  Purchase #7 $230.95   5.340%   $243.2827   $243.28   $243.30   $243.30  
  7 purchase totals = $919.30       $987.7632   $987.76   $987.80   $987.70