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 $70.42   10.512%   $77.8226   $77.82   $77.80   $77.80  
  Purchase #2 $110.53   13.385%   $125.3244   $125.32   $125.30   $125.30  
  Purchase #3 $208.54   11.562%   $232.6514   $232.65   $232.65   $232.70  
  Purchase #4 $167.49   3.492%   $173.3388   $173.34   $173.35   $173.30  
  Purchase #5 $81.70   5.756%   $86.4027   $86.40   $86.40   $86.40  
  Purchase #6 $29.68   9.752%   $32.5744   $32.57   $32.55   $32.60  
  Purchase #7 $44.47   8.433%   $48.2202   $48.22   $48.20   $48.20  
  7 purchase totals = $712.83       $776.3345   $776.32   $776.25   $776.30