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 $61.36   13.352%   $69.5528   $69.55   $69.55   $69.60  
  Purchase #2 $122.49   11.716%   $136.8409   $136.84   $136.85   $136.80  
  Purchase #3 $198.37   8.316%   $214.8664   $214.87   $214.85   $214.90  
  Purchase #4 $212.88   8.739%   $231.4836   $231.48   $231.50   $231.50  
  Purchase #5 $168.95   5.316%   $177.9314   $177.93   $177.95   $177.90  
  Purchase #6 $62.79   12.102%   $70.3888   $70.39   $70.40   $70.40  
  Purchase #7 $227.61   8.234%   $246.3514   $246.35   $246.35   $246.40  
  7 purchase totals = $1,054.45       $1,147.4153   $1,147.41   $1,147.45   $1,147.50