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 $176.83   10.806%   $195.9382   $195.94   $195.95   $195.90  
  Purchase #2 $102.41   7.430%   $110.0191   $110.02   $110.00   $110.00  
  Purchase #3 $250.83   4.699%   $262.6165   $262.62   $262.60   $262.60  
  Purchase #4 $187.47   8.838%   $204.0386   $204.04   $204.05   $204.00  
  Purchase #5 $196.66   4.411%   $205.3347   $205.33   $205.35   $205.30  
  Purchase #6 $107.39   4.558%   $112.2848   $112.28   $112.30   $112.30  
  Purchase #7 $223.58   3.344%   $231.0565   $231.06   $231.05   $231.10  
  7 purchase totals = $1,245.17       $1,321.2884   $1,321.29   $1,321.30   $1,321.20