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 $68.25   7.436%   $73.3251   $73.33   $73.35   $73.30  
  Purchase #2 $57.55   7.854%   $62.07   $62.07   $62.05   $62.10  
  Purchase #3 $250.69   6.573%   $267.1679   $267.17   $267.15   $267.20  
  Purchase #4 $80.67   13.698%   $91.7202   $91.72   $91.70   $91.70  
  Purchase #5 $48.92   11.274%   $54.4352   $54.44   $54.45   $54.40  
  Purchase #6 $118.34   13.755%   $134.6177   $134.62   $134.60   $134.60  
  Purchase #7 $85.67   5.819%   $90.6551   $90.66   $90.65   $90.70  
  7 purchase totals = $710.09       $773.9912   $774.01   $773.95   $774.00