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 $148.67   6.211%   $157.9039   $157.90   $157.90   $157.90  
  Purchase #2 $238.65   13.145%   $270.0205   $270.02   $270.00   $270.00  
  Purchase #3 $239.85   9.596%   $262.866   $262.87   $262.85   $262.90  
  Purchase #4 $223.93   6.215%   $237.8472   $237.85   $237.85   $237.80  
  Purchase #5 $51.44   8.206%   $55.6612   $55.66   $55.65   $55.70  
  Purchase #6 $240.66   10.235%   $265.2916   $265.29   $265.30   $265.30  
  Purchase #7 $24.25   8.687%   $26.3566   $26.36   $26.35   $26.40  
  7 purchase totals = $1,167.45       $1,275.9470   $1,275.95   $1,275.90   $1,276.00