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 $208.99   3.760%   $216.848   $216.85   $216.85   $216.80  
  Purchase #2 $64.27   3.268%   $66.3703   $66.37   $66.35   $66.40  
  Purchase #3 $20.28   13.578%   $23.0336   $23.03   $23.05   $23.00  
  Purchase #4 $223.48   10.512%   $246.9722   $246.97   $246.95   $247.00  
  Purchase #5 $157.38   6.410%   $167.4681   $167.47   $167.45   $167.50  
  Purchase #6 $41.90   10.114%   $46.1378   $46.14   $46.15   $46.10  
  Purchase #7 $86.71   9.439%   $94.8946   $94.89   $94.90   $94.90  
  7 purchase totals = $803.01       $861.7246   $861.72   $861.70   $861.70