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 $196.31   11.231%   $218.3576   $218.36   $218.35   $218.40  
  Purchase #2 $156.92   8.874%   $170.8451   $170.85   $170.85   $170.80  
  Purchase #3 $33.58   11.616%   $37.4807   $37.48   $37.50   $37.50  
  Purchase #4 $194.64   10.653%   $215.375   $215.38   $215.40   $215.40  
  Purchase #5 $56.94   8.441%   $61.7463   $61.75   $61.75   $61.70  
  Purchase #6 $250.27   13.536%   $284.1465   $284.15   $284.15   $284.10  
  Purchase #7 $23.73   8.123%   $25.6576   $25.66   $25.65   $25.70  
  7 purchase totals = $912.39       $1,013.6088   $1,013.63   $1,013.65   $1,013.60