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 $167.90   11.731%   $187.5963   $187.60   $187.60   $187.60  
  Purchase #2 $233.74   11.275%   $260.0942   $260.09   $260.10   $260.10  
  Purchase #3 $187.70   6.398%   $199.709   $199.71   $199.70   $199.70  
  Purchase #4 $228.31   5.520%   $240.9127   $240.91   $240.90   $240.90  
  Purchase #5 $196.44   9.172%   $214.4575   $214.46   $214.45   $214.50  
  Purchase #6 $44.76   3.373%   $46.2698   $46.27   $46.25   $46.30  
  Purchase #7 $68.31   6.566%   $72.7952   $72.80   $72.80   $72.80  
  7 purchase totals = $1,127.16       $1,221.8347   $1,221.84   $1,221.80   $1,221.90