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 $168.84   11.187%   $187.7281   $187.73   $187.75   $187.70  
  Purchase #2 $226.55   9.427%   $247.9069   $247.91   $247.90   $247.90  
  Purchase #3 $39.28   13.526%   $44.593   $44.59   $44.60   $44.60  
  Purchase #4 $64.48   3.823%   $66.9451   $66.95   $66.95   $66.90  
  Purchase #5 $115.77   13.623%   $131.5413   $131.54   $131.55   $131.50  
  Purchase #6 $77.32   3.164%   $79.7664   $79.77   $79.75   $79.80  
  Purchase #7 $170.38   8.448%   $184.7737   $184.77   $184.75   $184.80  
  7 purchase totals = $862.62       $943.2545   $943.26   $943.25   $943.20