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 $91.67   12.534%   $103.1599   $103.16   $103.15   $103.20  
  Purchase #2 $71.78   6.126%   $76.1772   $76.18   $76.20   $76.20  
  Purchase #3 $80.90   13.139%   $91.5295   $91.53   $91.55   $91.50  
  Purchase #4 $126.46   4.185%   $131.7524   $131.75   $131.75   $131.80  
  Purchase #5 $201.47   9.331%   $220.2692   $220.27   $220.25   $220.30  
  Purchase #6 $65.93   6.676%   $70.3315   $70.33   $70.35   $70.30  
  Purchase #7 $85.74   3.131%   $88.4245   $88.42   $88.40   $88.40  
  7 purchase totals = $723.95       $781.6442   $781.64   $781.65   $781.70