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 $95.76   6.331%   $101.8226   $101.82   $101.80   $101.80  
  Purchase #2 $44.99   9.415%   $49.2258   $49.23   $49.25   $49.20  
  Purchase #3 $199.50   7.745%   $214.9513   $214.95   $214.95   $215.00  
  Purchase #4 $26.64   11.855%   $29.7982   $29.80   $29.80   $29.80  
  Purchase #5 $241.86   6.603%   $257.83   $257.83   $257.85   $257.80  
  Purchase #6 $85.41   8.419%   $92.6007   $92.60   $92.60   $92.60  
  Purchase #7 $111.83   6.655%   $119.2723   $119.27   $119.25   $119.30  
  7 purchase totals = $805.99       $865.5009   $865.50   $865.50   $865.50