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 $141.61   12.206%   $158.8949   $158.89   $158.90   $158.90  
  Purchase #2 $221.56   11.646%   $247.3629   $247.36   $247.35   $247.40  
  Purchase #3 $116.68   4.515%   $121.9481   $121.95   $121.95   $121.90  
  Purchase #4 $174.69   7.819%   $188.349   $188.35   $188.35   $188.30  
  Purchase #5 $212.37   12.727%   $239.3983   $239.40   $239.40   $239.40  
  Purchase #6 $186.89   9.675%   $204.9716   $204.97   $204.95   $205.00  
  Purchase #7 $71.26   13.429%   $80.8295   $80.83   $80.85   $80.80  
  7 purchase totals = $1,125.06       $1,241.7543   $1,241.75   $1,241.75   $1,241.70