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 $70.59   4.115%   $73.4948   $73.49   $73.50   $73.50  
  Purchase #2 $179.25   9.144%   $195.6406   $195.64   $195.65   $195.60  
  Purchase #3 $162.38   11.595%   $181.208   $181.21   $181.20   $181.20  
  Purchase #4 $194.75   6.540%   $207.4867   $207.49   $207.50   $207.50  
  Purchase #5 $16.35   4.725%   $17.1225   $17.12   $17.10   $17.10  
  Purchase #6 $160.66   4.248%   $167.4848   $167.48   $167.50   $167.50  
  Purchase #7 $25.84   4.495%   $27.0015   $27.00   $27.00   $27.00  
  7 purchase totals = $809.82       $869.4389   $869.43   $869.45   $869.40