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 $88.66   5.835%   $93.8333   $93.83   $93.85   $93.80  
  Purchase #2 $14.72   13.716%   $16.739   $16.74   $16.75   $16.70  
  Purchase #3 $89.39   6.250%   $94.9769   $94.98   $95.00   $95.00  
  Purchase #4 $109.50   4.763%   $114.7155   $114.72   $114.70   $114.70  
  Purchase #5 $79.60   13.298%   $90.1852   $90.19   $90.20   $90.20  
  Purchase #6 $11.73   10.438%   $12.9544   $12.95   $12.95   $13.00  
  Purchase #7 $148.75   3.799%   $154.401   $154.40   $154.40   $154.40  
  7 purchase totals = $542.35       $577.8053   $577.81   $577.85   $577.80