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 $216.92   10.333%   $239.3343   $239.33   $239.35   $239.30  
  Purchase #2 $86.31   6.448%   $91.8753   $91.88   $91.90   $91.90  
  Purchase #3 $49.93   3.183%   $51.5193   $51.52   $51.50   $51.50  
  Purchase #4 $47.44   11.272%   $52.7874   $52.79   $52.80   $52.80  
  Purchase #5 $216.29   6.297%   $229.9098   $229.91   $229.90   $229.90  
  Purchase #6 $192.79   5.795%   $203.9622   $203.96   $203.95   $204.00  
  Purchase #7 $75.36   3.480%   $77.9825   $77.98   $78.00   $78.00  
  7 purchase totals = $885.04       $947.3708   $947.37   $947.40   $947.40