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 $245.65   8.807%   $267.2844   $267.28   $267.30   $267.30  
  Purchase #2 $42.76   9.223%   $46.7038   $46.70   $46.70   $46.70  
  Purchase #3 $178.71   6.653%   $190.5996   $190.60   $190.60   $190.60  
  Purchase #4 $243.81   9.625%   $267.2767   $267.28   $267.30   $267.30  
  Purchase #5 $191.79   9.841%   $210.6641   $210.66   $210.65   $210.70  
  Purchase #6 $231.99   7.127%   $248.5239   $248.52   $248.50   $248.50  
  Purchase #7 $89.44   13.328%   $101.3606   $101.36   $101.35   $101.40  
  7 purchase totals = $1,224.15       $1,332.4131   $1,332.40   $1,332.40   $1,332.50