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 $71.54   5.122%   $75.2043   $75.20   $75.20   $75.20  
  Purchase #2 $123.45   11.662%   $137.8467   $137.85   $137.85   $137.80  
  Purchase #3 $125.76   4.152%   $130.9816   $130.98   $131.00   $131.00  
  Purchase #4 $57.95   5.719%   $61.2642   $61.26   $61.25   $61.30  
  Purchase #5 $222.26   9.414%   $243.1836   $243.18   $243.20   $243.20  
  Purchase #6 $207.96   4.205%   $216.7047   $216.70   $216.70   $216.70  
  Purchase #7 $88.96   3.366%   $91.9544   $91.95   $91.95   $92.00  
  7 purchase totals = $897.88       $957.1395   $957.12   $957.15   $957.20