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 $61.35   11.116%   $68.1697   $68.17   $68.15   $68.20  
  Purchase #2 $247.53   3.123%   $255.2604   $255.26   $255.25   $255.30  
  Purchase #3 $135.35   4.802%   $141.8495   $141.85   $141.85   $141.80  
  Purchase #4 $35.36   8.267%   $38.2832   $38.28   $38.30   $38.30  
  Purchase #5 $61.28   9.655%   $67.1966   $67.20   $67.20   $67.20  
  Purchase #6 $92.69   6.702%   $98.9021   $98.90   $98.90   $98.90  
  Purchase #7 $22.27   6.597%   $23.7392   $23.74   $23.75   $23.70  
  7 purchase totals = $655.83       $693.4007   $693.40   $693.40   $693.40