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 $93.34   10.306%   $102.9596   $102.96   $102.95   $103.00  
  Purchase #2 $53.61   13.407%   $60.7975   $60.80   $60.80   $60.80  
  Purchase #3 $201.49   13.864%   $229.4246   $229.42   $229.40   $229.40  
  Purchase #4 $228.34   11.613%   $254.8571   $254.86   $254.85   $254.90  
  Purchase #5 $57.40   5.255%   $60.4164   $60.42   $60.40   $60.40  
  Purchase #6 $23.78   7.250%   $25.5041   $25.50   $25.50   $25.50  
  Purchase #7 $36.98   8.146%   $39.9924   $39.99   $40.00   $40.00  
  7 purchase totals = $694.94       $773.9517   $773.95   $773.90   $774.00