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 $206.94   12.682%   $233.1841   $233.18   $233.20   $233.20  
  Purchase #2 $70.80   4.121%   $73.7177   $73.72   $73.70   $73.70  
  Purchase #3 $169.71   12.552%   $191.012   $191.01   $191.00   $191.00  
  Purchase #4 $192.86   6.307%   $205.0237   $205.02   $205.00   $205.00  
  Purchase #5 $73.59   4.572%   $76.9545   $76.95   $76.95   $77.00  
  Purchase #6 $17.38   7.155%   $18.6235   $18.62   $18.60   $18.60  
  Purchase #7 $140.92   8.805%   $153.328   $153.33   $153.35   $153.30  
  7 purchase totals = $872.20       $951.8435   $951.83   $951.80   $951.80