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 $241.61   10.112%   $266.0416   $266.04   $266.05   $266.00  
  Purchase #2 $112.55   6.231%   $119.563   $119.56   $119.55   $119.60  
  Purchase #3 $79.72   5.802%   $84.3454   $84.35   $84.35   $84.30  
  Purchase #4 $94.32   12.411%   $106.0261   $106.03   $106.05   $106.00  
  Purchase #5 $58.99   4.137%   $61.4304   $61.43   $61.45   $61.40  
  Purchase #6 $127.79   3.655%   $132.4607   $132.46   $132.45   $132.50  
  Purchase #7 $21.99   3.789%   $22.8232   $22.82   $22.80   $22.80  
  7 purchase totals = $736.97       $792.6904   $792.69   $792.70   $792.60