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 $149.63   12.277%   $168.0001   $168.00   $168.00   $168.00  
  Purchase #2 $143.54   6.377%   $152.6935   $152.69   $152.70   $152.70  
  Purchase #3 $174.95   8.746%   $190.2511   $190.25   $190.25   $190.30  
  Purchase #4 $68.77   9.431%   $75.2557   $75.26   $75.25   $75.30  
  Purchase #5 $239.67   12.575%   $269.8085   $269.81   $269.80   $269.80  
  Purchase #6 $62.30   3.163%   $64.2705   $64.27   $64.25   $64.30  
  Purchase #7 $244.91   12.802%   $276.2634   $276.26   $276.25   $276.30  
  7 purchase totals = $1,083.77       $1,196.5428   $1,196.54   $1,196.50   $1,196.70