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 $203.60   11.461%   $226.9346   $226.93   $226.95   $226.90  
  Purchase #2 $30.45   13.109%   $34.4417   $34.44   $34.45   $34.40  
  Purchase #3 $45.88   7.154%   $49.1623   $49.16   $49.15   $49.20  
  Purchase #4 $69.86   4.557%   $73.0435   $73.04   $73.05   $73.00  
  Purchase #5 $185.49   10.523%   $205.0091   $205.01   $205.00   $205.00  
  Purchase #6 $110.55   10.374%   $122.0185   $122.02   $122.00   $122.00  
  Purchase #7 $47.72   3.429%   $49.3563   $49.36   $49.35   $49.40  
  7 purchase totals = $693.55       $759.9660   $759.96   $759.95   $759.90