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 $65.87   11.238%   $73.2725   $73.27   $73.25   $73.30  
  Purchase #2 $137.98   10.670%   $152.7025   $152.70   $152.70   $152.70  
  Purchase #3 $107.26   9.713%   $117.6782   $117.68   $117.70   $117.70  
  Purchase #4 $183.30   9.584%   $200.8675   $200.87   $200.85   $200.90  
  Purchase #5 $8.85   13.291%   $10.0263   $10.03   $10.05   $10.00  
  Purchase #6 $208.43   11.665%   $232.7434   $232.74   $232.75   $232.70  
  Purchase #7 $25.50   5.590%   $26.9255   $26.93   $26.95   $26.90  
  7 purchase totals = $737.19       $814.2159   $814.22   $814.25   $814.20