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 $58.73   11.700%   $65.6014   $65.60   $65.60   $65.60  
  Purchase #2 $196.97   8.854%   $214.4097   $214.41   $214.40   $214.40  
  Purchase #3 $222.49   9.425%   $243.4597   $243.46   $243.45   $243.50  
  Purchase #4 $194.86   13.278%   $220.7335   $220.73   $220.75   $220.70  
  Purchase #5 $53.79   5.343%   $56.664   $56.66   $56.65   $56.70  
  Purchase #6 $94.71   3.526%   $98.0495   $98.05   $98.05   $98.00  
  Purchase #7 $83.55   12.793%   $94.2386   $94.24   $94.25   $94.20  
  7 purchase totals = $905.10       $993.1564   $993.15   $993.15   $993.10