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 $246.55   8.200%   $266.7671   $266.77   $266.75   $266.80  
  Purchase #2 $108.85   10.197%   $119.9494   $119.95   $119.95   $119.90  
  Purchase #3 $246.35   5.158%   $259.0567   $259.06   $259.05   $259.10  
  Purchase #4 $103.80   3.706%   $107.6468   $107.65   $107.65   $107.60  
  Purchase #5 $51.39   13.380%   $58.266   $58.27   $58.25   $58.30  
  Purchase #6 $84.89   7.542%   $91.2924   $91.29   $91.30   $91.30  
  Purchase #7 $67.73   5.130%   $71.2045   $71.20   $71.20   $71.20  
  7 purchase totals = $909.56       $974.1829   $974.19   $974.15   $974.20