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 $132.63   9.137%   $144.7484   $144.75   $144.75   $144.70  
  Purchase #2 $39.99   6.451%   $42.5698   $42.57   $42.55   $42.60  
  Purchase #3 $113.32   8.771%   $123.2593   $123.26   $123.25   $123.30  
  Purchase #4 $243.94   4.216%   $254.2245   $254.22   $254.20   $254.20  
  Purchase #5 $65.68   9.546%   $71.9498   $71.95   $71.95   $71.90  
  Purchase #6 $203.63   4.206%   $212.1947   $212.19   $212.20   $212.20  
  Purchase #7 $147.74   11.506%   $164.739   $164.74   $164.75   $164.70  
  7 purchase totals = $946.93       $1,013.6855   $1,013.68   $1,013.65   $1,013.60