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 $76.83   7.143%   $82.318   $82.32   $82.30   $82.30  
  Purchase #2 $90.38   10.231%   $99.6268   $99.63   $99.65   $99.60  
  Purchase #3 $175.55   4.551%   $183.5393   $183.54   $183.55   $183.50  
  Purchase #4 $108.30   13.449%   $122.8653   $122.87   $122.85   $122.90  
  Purchase #5 $237.99   12.594%   $267.9625   $267.96   $267.95   $268.00  
  Purchase #6 $228.27   6.633%   $243.4111   $243.41   $243.40   $243.40  
  Purchase #7 $70.82   4.345%   $73.8971   $73.90   $73.90   $73.90  
  7 purchase totals = $988.14       $1,073.6201   $1,073.63   $1,073.60   $1,073.60