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 $202.99   6.636%   $216.4604   $216.46   $216.45   $216.50  
  Purchase #2 $60.84   10.650%   $67.3195   $67.32   $67.30   $67.30  
  Purchase #3 $31.54   5.531%   $33.2845   $33.28   $33.30   $33.30  
  Purchase #4 $96.91   5.803%   $102.5337   $102.53   $102.55   $102.50  
  Purchase #5 $126.40   13.188%   $143.0696   $143.07   $143.05   $143.10  
  Purchase #6 $221.26   4.813%   $231.9092   $231.91   $231.90   $231.90  
  Purchase #7 $161.74   8.182%   $174.9736   $174.97   $174.95   $175.00  
  7 purchase totals = $901.68       $969.5505   $969.54   $969.50   $969.60