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 $34.56   4.839%   $36.2324   $36.23   $36.25   $36.20  
  Purchase #2 $154.45   3.144%   $159.3059   $159.31   $159.30   $159.30  
  Purchase #3 $69.60   4.750%   $72.906   $72.91   $72.90   $72.90  
  Purchase #4 $188.38   4.835%   $197.4882   $197.49   $197.50   $197.50  
  Purchase #5 $169.38   12.629%   $190.771   $190.77   $190.75   $190.80  
  Purchase #6 $184.92   10.818%   $204.9246   $204.92   $204.90   $204.90  
  Purchase #7 $9.30   3.842%   $9.6573   $9.66   $9.65   $9.70  
  7 purchase totals = $810.59       $871.2854   $871.29   $871.25   $871.30