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 $218.91   10.391%   $241.6569   $241.66   $241.65   $241.70  
  Purchase #2 $238.77   13.399%   $270.7628   $270.76   $270.75   $270.80  
  Purchase #3 $56.53   13.401%   $64.1056   $64.11   $64.10   $64.10  
  Purchase #4 $156.93   10.442%   $173.3166   $173.32   $173.30   $173.30  
  Purchase #5 $180.73   7.525%   $194.3299   $194.33   $194.35   $194.30  
  Purchase #6 $245.74   8.141%   $265.7457   $265.75   $265.75   $265.70  
  Purchase #7 $246.30   5.604%   $260.1027   $260.10   $260.10   $260.10  
  7 purchase totals = $1,343.91       $1,470.0202   $1,470.03   $1,470.00   $1,470.00