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 $90.86   6.525%   $96.7886   $96.79   $96.80   $96.80  
  Purchase #2 $53.63   5.662%   $56.6665   $56.67   $56.65   $56.70  
  Purchase #3 $48.37   4.289%   $50.4446   $50.44   $50.45   $50.40  
  Purchase #4 $162.75   13.589%   $184.8661   $184.87   $184.85   $184.90  
  Purchase #5 $238.92   4.473%   $249.6069   $249.61   $249.60   $249.60  
  Purchase #6 $228.47   13.258%   $258.7606   $258.76   $258.75   $258.80  
  Purchase #7 $170.32   4.189%   $177.4547   $177.45   $177.45   $177.50  
  7 purchase totals = $993.32       $1,074.5880   $1,074.59   $1,074.55   $1,074.70