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 $84.74   9.176%   $92.5157   $92.52   $92.50   $92.50  
  Purchase #2 $157.27   9.130%   $171.6288   $171.63   $171.65   $171.60  
  Purchase #3 $231.68   4.778%   $242.7497   $242.75   $242.75   $242.70  
  Purchase #4 $235.98   13.781%   $268.5004   $268.50   $268.50   $268.50  
  Purchase #5 $215.95   11.809%   $241.4515   $241.45   $241.45   $241.50  
  Purchase #6 $208.98   13.220%   $236.6072   $236.61   $236.60   $236.60  
  Purchase #7 $18.47   4.321%   $19.2681   $19.27   $19.25   $19.30  
  7 purchase totals = $1,153.07       $1,272.7214   $1,272.73   $1,272.70   $1,272.70