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 $174.97   5.846%   $185.1987   $185.20   $185.20   $185.20  
  Purchase #2 $250.33   4.449%   $261.4672   $261.47   $261.45   $261.50  
  Purchase #3 $6.94   7.300%   $7.4466   $7.45   $7.45   $7.40  
  Purchase #4 $124.78   9.345%   $136.4407   $136.44   $136.45   $136.40  
  Purchase #5 $186.65   8.235%   $202.0206   $202.02   $202.00   $202.00  
  Purchase #6 $155.40   7.677%   $167.3301   $167.33   $167.35   $167.30  
  Purchase #7 $244.61   4.412%   $255.4022   $255.40   $255.40   $255.40  
  7 purchase totals = $1,143.68       $1,215.3061   $1,215.31   $1,215.30   $1,215.20