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 $61.47   9.510%   $67.3158   $67.32   $67.30   $67.30  
  Purchase #2 $203.25   13.156%   $229.9896   $229.99   $230.00   $230.00  
  Purchase #3 $181.79   5.305%   $191.434   $191.43   $191.45   $191.40  
  Purchase #4 $24.86   10.624%   $27.5011   $27.50   $27.50   $27.50  
  Purchase #5 $178.87   11.606%   $199.6297   $199.63   $199.65   $199.60  
  Purchase #6 $23.86   3.593%   $24.7173   $24.72   $24.70   $24.70  
  Purchase #7 $249.26   9.395%   $272.678   $272.68   $272.70   $272.70  
  7 purchase totals = $923.36       $1,013.2655   $1,013.27   $1,013.30   $1,013.20