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 $204.44   10.653%   $226.219   $226.22   $226.20   $226.20  
  Purchase #2 $45.43   5.833%   $48.0799   $48.08   $48.10   $48.10  
  Purchase #3 $7.29   5.561%   $7.6954   $7.70   $7.70   $7.70  
  Purchase #4 $83.54   6.555%   $89.016   $89.02   $89.00   $89.00  
  Purchase #5 $182.29   10.778%   $201.9372   $201.94   $201.95   $201.90  
  Purchase #6 $136.35   5.863%   $144.3442   $144.34   $144.35   $144.30  
  Purchase #7 $170.73   9.243%   $186.5106   $186.51   $186.50   $186.50  
  7 purchase totals = $830.07       $903.8023   $903.81   $903.80   $903.70