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 $34.86   5.727%   $36.8564   $36.86   $36.85   $36.90  
  Purchase #2 $15.49   11.866%   $17.328   $17.33   $17.35   $17.30  
  Purchase #3 $174.83   5.624%   $184.6624   $184.66   $184.65   $184.70  
  Purchase #4 $228.67   9.848%   $251.1894   $251.19   $251.20   $251.20  
  Purchase #5 $118.89   8.110%   $128.532   $128.53   $128.55   $128.50  
  Purchase #6 $187.34   5.707%   $198.0315   $198.03   $198.05   $198.00  
  Purchase #7 $48.86   4.458%   $51.0382   $51.04   $51.05   $51.00  
  7 purchase totals = $808.94       $867.6379   $867.64   $867.70   $867.60