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 $146.68   6.281%   $155.893   $155.89   $155.90   $155.90  
  Purchase #2 $212.48   5.188%   $223.5035   $223.50   $223.50   $223.50  
  Purchase #3 $24.92   9.686%   $27.3338   $27.33   $27.35   $27.30  
  Purchase #4 $92.26   10.543%   $101.987   $101.99   $102.00   $102.00  
  Purchase #5 $11.38   8.249%   $12.3187   $12.32   $12.30   $12.30  
  Purchase #6 $165.86   12.512%   $186.6124   $186.61   $186.60   $186.60  
  Purchase #7 $153.59   5.496%   $162.0313   $162.03   $162.05   $162.00  
  7 purchase totals = $807.17       $869.6797   $869.67   $869.70   $869.60