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 $34.78   4.505%   $36.3468   $36.35   $36.35   $36.30  
  Purchase #2 $102.62   8.607%   $111.4525   $111.45   $111.45   $111.50  
  Purchase #3 $68.26   8.309%   $73.9317   $73.93   $73.95   $73.90  
  Purchase #4 $82.49   4.259%   $86.0032   $86.00   $86.00   $86.00  
  Purchase #5 $8.84   9.685%   $9.6962   $9.70   $9.70   $9.70  
  Purchase #6 $13.32   5.233%   $14.017   $14.02   $14.00   $14.00  
  Purchase #7 $244.71   12.331%   $274.8852   $274.89   $274.90   $274.90  
  7 purchase totals = $555.02       $606.3326   $606.34   $606.35   $606.30