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 $174.46   6.769%   $186.2692   $186.27   $186.25   $186.30  
  Purchase #2 $55.44   5.407%   $58.4376   $58.44   $58.45   $58.40  
  Purchase #3 $121.41   7.821%   $130.9055   $130.91   $130.90   $130.90  
  Purchase #4 $152.98   7.589%   $164.5897   $164.59   $164.60   $164.60  
  Purchase #5 $79.34   10.514%   $87.6818   $87.68   $87.70   $87.70  
  Purchase #6 $128.42   12.591%   $144.5894   $144.59   $144.60   $144.60  
  Purchase #7 $230.44   8.425%   $249.8546   $249.85   $249.85   $249.90  
  7 purchase totals = $942.49       $1,022.3278   $1,022.33   $1,022.35   $1,022.40