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 $250.92   10.203%   $276.5214   $276.52   $276.50   $276.50  
  Purchase #2 $152.28   6.598%   $162.3274   $162.33   $162.35   $162.30  
  Purchase #3 $123.47   11.511%   $137.6826   $137.68   $137.70   $137.70  
  Purchase #4 $65.70   12.137%   $73.674   $73.67   $73.65   $73.70  
  Purchase #5 $9.35   5.272%   $9.8429   $9.84   $9.85   $9.80  
  Purchase #6 $168.31   9.795%   $184.796   $184.80   $184.80   $184.80  
  Purchase #7 $199.68   11.590%   $222.8229   $222.82   $222.80   $222.80  
  7 purchase totals = $969.71       $1,067.6672   $1,067.66   $1,067.65   $1,067.60