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 $223.94   10.858%   $248.2554   $248.26   $248.25   $248.30  
  Purchase #2 $79.47   10.269%   $87.6308   $87.63   $87.65   $87.60  
  Purchase #3 $145.91   13.595%   $165.7465   $165.75   $165.75   $165.70  
  Purchase #4 $149.91   9.458%   $164.0885   $164.09   $164.10   $164.10  
  Purchase #5 $220.36   11.585%   $245.8887   $245.89   $245.90   $245.90  
  Purchase #6 $61.97   7.579%   $66.6667   $66.67   $66.65   $66.70  
  Purchase #7 $72.83   12.809%   $82.1588   $82.16   $82.15   $82.20  
  7 purchase totals = $954.39       $1,060.4354   $1,060.45   $1,060.45   $1,060.50