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 $178.63   13.656%   $203.0237   $203.02   $203.00   $203.00  
  Purchase #2 $238.81   8.515%   $259.1447   $259.14   $259.15   $259.10  
  Purchase #3 $62.59   7.673%   $67.3925   $67.39   $67.40   $67.40  
  Purchase #4 $178.98   11.717%   $199.9511   $199.95   $199.95   $200.00  
  Purchase #5 $61.53   7.181%   $65.9485   $65.95   $65.95   $65.90  
  Purchase #6 $218.55   8.579%   $237.2994   $237.30   $237.30   $237.30  
  Purchase #7 $200.82   12.757%   $226.4386   $226.44   $226.45   $226.40  
  7 purchase totals = $1,139.91       $1,259.1985   $1,259.19   $1,259.20   $1,259.10