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 $82.73   12.703%   $93.2392   $93.24   $93.25   $93.20  
  Purchase #2 $182.28   13.160%   $206.268   $206.27   $206.25   $206.30  
  Purchase #3 $115.60   9.211%   $126.2479   $126.25   $126.25   $126.20  
  Purchase #4 $91.90   4.572%   $96.1017   $96.10   $96.10   $96.10  
  Purchase #5 $163.75   3.405%   $169.3257   $169.33   $169.35   $169.30  
  Purchase #6 $189.73   12.665%   $213.7593   $213.76   $213.75   $213.80  
  Purchase #7 $142.96   6.300%   $151.9665   $151.97   $151.95   $152.00  
  7 purchase totals = $968.95       $1,056.9083   $1,056.92   $1,056.90   $1,056.90