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 $246.66   8.145%   $266.7505   $266.75   $266.75   $266.80  
  Purchase #2 $217.58   8.211%   $235.4455   $235.45   $235.45   $235.40  
  Purchase #3 $208.29   11.629%   $232.512   $232.51   $232.50   $232.50  
  Purchase #4 $190.61   8.489%   $206.7909   $206.79   $206.80   $206.80  
  Purchase #5 $56.76   10.784%   $62.881   $62.88   $62.90   $62.90  
  Purchase #6 $76.92   5.170%   $80.8968   $80.90   $80.90   $80.90  
  Purchase #7 $202.25   5.359%   $213.0886   $213.09   $213.10   $213.10  
  7 purchase totals = $1,199.07       $1,298.3653   $1,298.37   $1,298.40   $1,298.40