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 $22.94   13.561%   $26.0509   $26.05   $26.05   $26.10  
  Purchase #2 $172.80   6.784%   $184.5228   $184.52   $184.50   $184.50  
  Purchase #3 $111.41   7.563%   $119.8359   $119.84   $119.85   $119.80  
  Purchase #4 $77.43   5.123%   $81.3967   $81.40   $81.40   $81.40  
  Purchase #5 $135.84   3.113%   $140.0687   $140.07   $140.05   $140.10  
  Purchase #6 $242.29   5.851%   $256.4664   $256.47   $256.45   $256.50  
  Purchase #7 $119.39   5.530%   $125.9923   $125.99   $126.00   $126.00  
  7 purchase totals = $882.10       $934.3337   $934.34   $934.30   $934.40