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 $62.72   12.725%   $70.7011   $70.70   $70.70   $70.70  
  Purchase #2 $179.99   13.871%   $204.9564   $204.96   $204.95   $205.00  
  Purchase #3 $217.89   13.338%   $246.9522   $246.95   $246.95   $247.00  
  Purchase #4 $173.74   12.327%   $195.1569   $195.16   $195.15   $195.20  
  Purchase #5 $131.96   7.191%   $141.4492   $141.45   $141.45   $141.40  
  Purchase #6 $221.34   10.553%   $244.698   $244.70   $244.70   $244.70  
  Purchase #7 $85.77   12.368%   $96.378   $96.38   $96.40   $96.40  
  7 purchase totals = $1,073.41       $1,200.2918   $1,200.30   $1,200.30   $1,200.40