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 $179.81   12.276%   $201.8835   $201.88   $201.90   $201.90  
  Purchase #2 $49.39   8.395%   $53.5363   $53.54   $53.55   $53.50  
  Purchase #3 $218.66   8.251%   $236.7016   $236.70   $236.70   $236.70  
  Purchase #4 $133.45   9.246%   $145.7888   $145.79   $145.80   $145.80  
  Purchase #5 $101.80   13.819%   $115.8677   $115.87   $115.85   $115.90  
  Purchase #6 $229.68   3.852%   $238.5273   $238.53   $238.55   $238.50  
  Purchase #7 $230.33   10.143%   $253.6924   $253.69   $253.70   $253.70  
  7 purchase totals = $1,143.12       $1,245.9976   $1,246.00   $1,246.05   $1,246.00