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 $174.76   6.848%   $186.7276   $186.73   $186.75   $186.70  
  Purchase #2 $235.28   7.853%   $253.7565   $253.76   $253.75   $253.80  
  Purchase #3 $116.82   13.165%   $132.1994   $132.20   $132.20   $132.20  
  Purchase #4 $162.65   6.135%   $172.6286   $172.63   $172.65   $172.60  
  Purchase #5 $61.91   4.127%   $64.465   $64.47   $64.45   $64.50  
  Purchase #6 $90.68   7.192%   $97.2017   $97.20   $97.20   $97.20  
  Purchase #7 $148.42   8.209%   $160.6038   $160.60   $160.60   $160.60  
  7 purchase totals = $990.52       $1,067.5826   $1,067.59   $1,067.60   $1,067.60