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 $31.36   10.145%   $34.5415   $34.54   $34.55   $34.50  
  Purchase #2 $229.59   8.473%   $249.0432   $249.04   $249.05   $249.00  
  Purchase #3 $49.59   11.467%   $55.2765   $55.28   $55.30   $55.30  
  Purchase #4 $157.52   10.381%   $173.8722   $173.87   $173.85   $173.90  
  Purchase #5 $182.86   8.614%   $198.6116   $198.61   $198.60   $198.60  
  Purchase #6 $116.61   8.547%   $126.5767   $126.58   $126.60   $126.60  
  Purchase #7 $176.66   7.175%   $189.3354   $189.34   $189.35   $189.30  
  7 purchase totals = $944.19       $1,027.2571   $1,027.26   $1,027.30   $1,027.20