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 $60.48   6.874%   $64.6374   $64.64   $64.65   $64.60  
  Purchase #2 $205.76   11.326%   $229.0644   $229.06   $229.05   $229.10  
  Purchase #3 $126.75   4.514%   $132.4715   $132.47   $132.45   $132.50  
  Purchase #4 $230.37   4.478%   $240.686   $240.69   $240.70   $240.70  
  Purchase #5 $54.81   10.652%   $60.6484   $60.65   $60.65   $60.60  
  Purchase #6 $122.47   8.533%   $132.9204   $132.92   $132.90   $132.90  
  Purchase #7 $165.31   11.333%   $184.0446   $184.04   $184.05   $184.00  
  7 purchase totals = $965.95       $1,044.4727   $1,044.47   $1,044.45   $1,044.40