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 $92.47   4.193%   $96.3473   $96.35   $96.35   $96.30  
  Purchase #2 $110.50   4.394%   $115.3554   $115.36   $115.35   $115.40  
  Purchase #3 $185.46   8.374%   $200.9904   $200.99   $201.00   $201.00  
  Purchase #4 $126.90   13.348%   $143.8386   $143.84   $143.85   $143.80  
  Purchase #5 $55.69   3.454%   $57.6135   $57.61   $57.60   $57.60  
  Purchase #6 $88.51   8.392%   $95.9378   $95.94   $95.95   $95.90  
  Purchase #7 $17.73   4.515%   $18.5305   $18.53   $18.55   $18.50  
  7 purchase totals = $677.26       $728.6135   $728.62   $728.65   $728.50