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   12.252%   $69.0013   $69.00   $69.00   $69.00  
  Purchase #2 $183.97   10.497%   $203.2813   $203.28   $203.30   $203.30  
  Purchase #3 $10.36   8.616%   $11.2526   $11.25   $11.25   $11.30  
  Purchase #4 $77.47   9.127%   $84.5407   $84.54   $84.55   $84.50  
  Purchase #5 $20.86   13.316%   $23.6377   $23.64   $23.65   $23.60  
  Purchase #6 $117.43   4.789%   $123.0537   $123.05   $123.05   $123.10  
  Purchase #7 $234.34   12.377%   $263.3443   $263.34   $263.35   $263.30  
  7 purchase totals = $705.90       $778.1116   $778.10   $778.15   $778.10