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 $61.71   12.173%   $69.222   $69.22   $69.20   $69.20  
  Purchase #2 $68.88   12.600%   $77.5589   $77.56   $77.55   $77.60  
  Purchase #3 $122.43   8.838%   $133.2504   $133.25   $133.25   $133.30  
  Purchase #4 $181.94   4.225%   $189.627   $189.63   $189.65   $189.60  
  Purchase #5 $115.48   12.548%   $129.9704   $129.97   $129.95   $130.00  
  Purchase #6 $234.48   3.608%   $242.94   $242.94   $242.95   $242.90  
  Purchase #7 $195.39   8.493%   $211.9845   $211.98   $212.00   $212.00  
  7 purchase totals = $980.31       $1,054.5532   $1,054.55   $1,054.55   $1,054.60