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 $241.97   4.610%   $253.1248   $253.12   $253.10   $253.10  
  Purchase #2 $63.82   11.149%   $70.9353   $70.94   $70.95   $70.90  
  Purchase #3 $154.66   7.212%   $165.8141   $165.81   $165.80   $165.80  
  Purchase #4 $226.64   10.718%   $250.9313   $250.93   $250.95   $250.90  
  Purchase #5 $96.86   4.405%   $101.1267   $101.13   $101.15   $101.10  
  Purchase #6 $76.80   3.115%   $79.1923   $79.19   $79.20   $79.20  
  Purchase #7 $222.29   7.515%   $238.9951   $239.00   $239.00   $239.00  
  7 purchase totals = $1,083.04       $1,160.1196   $1,160.12   $1,160.15   $1,160.00