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 $70.62   8.379%   $76.5372   $76.54   $76.55   $76.50  
  Purchase #2 $134.45   7.109%   $144.0081   $144.01   $144.00   $144.00  
  Purchase #3 $165.46   7.655%   $178.126   $178.13   $178.15   $178.10  
  Purchase #4 $58.53   5.749%   $61.8949   $61.89   $61.90   $61.90  
  Purchase #5 $76.70   7.720%   $82.6212   $82.62   $82.60   $82.60  
  Purchase #6 $246.88   10.726%   $273.3603   $273.36   $273.35   $273.40  
  Purchase #7 $197.40   8.237%   $213.6598   $213.66   $213.65   $213.70  
  7 purchase totals = $950.04       $1,030.2075   $1,030.21   $1,030.20   $1,030.20