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 $69.44   10.667%   $76.8472   $76.85   $76.85   $76.80  
  Purchase #2 $123.88   13.556%   $140.6732   $140.67   $140.65   $140.70  
  Purchase #3 $17.57   4.238%   $18.3146   $18.31   $18.30   $18.30  
  Purchase #4 $69.69   9.666%   $76.4262   $76.43   $76.45   $76.40  
  Purchase #5 $245.52   8.641%   $266.7354   $266.74   $266.75   $266.70  
  Purchase #6 $146.34   7.729%   $157.6506   $157.65   $157.65   $157.70  
  Purchase #7 $50.70   10.572%   $56.06   $56.06   $56.05   $56.10  
  7 purchase totals = $723.14       $792.7072   $792.71   $792.70   $792.70