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 $64.42   7.293%   $69.1182   $69.12   $69.10   $69.10  
  Purchase #2 $145.94   8.644%   $158.5551   $158.56   $158.55   $158.60  
  Purchase #3 $170.60   8.705%   $185.4507   $185.45   $185.45   $185.50  
  Purchase #4 $226.77   9.333%   $247.9344   $247.93   $247.95   $247.90  
  Purchase #5 $58.35   3.615%   $60.4594   $60.46   $60.45   $60.50  
  Purchase #6 $208.29   11.348%   $231.9267   $231.93   $231.95   $231.90  
  Purchase #7 $12.41   12.727%   $13.9894   $13.99   $14.00   $14.00  
  7 purchase totals = $886.78       $967.4339   $967.44   $967.45   $967.50