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 $236.97   12.549%   $266.7074   $266.71   $266.70   $266.70  
  Purchase #2 $137.36   8.203%   $148.6276   $148.63   $148.65   $148.60  
  Purchase #3 $120.81   5.462%   $127.4086   $127.41   $127.40   $127.40  
  Purchase #4 $77.59   10.294%   $85.5771   $85.58   $85.60   $85.60  
  Purchase #5 $14.62   7.115%   $15.6602   $15.66   $15.65   $15.70  
  Purchase #6 $214.46   9.768%   $235.4085   $235.41   $235.40   $235.40  
  Purchase #7 $147.74   6.142%   $156.8142   $156.81   $156.80   $156.80  
  7 purchase totals = $949.55       $1,036.2036   $1,036.21   $1,036.20   $1,036.20