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 $26.64   11.231%   $29.6319   $29.63   $29.65   $29.60  
  Purchase #2 $170.94   8.633%   $185.6973   $185.70   $185.70   $185.70  
  Purchase #3 $34.58   7.530%   $37.1839   $37.18   $37.20   $37.20  
  Purchase #4 $141.76   10.282%   $156.3358   $156.34   $156.35   $156.30  
  Purchase #5 $30.48   13.763%   $34.675   $34.68   $34.70   $34.70  
  Purchase #6 $189.43   10.536%   $209.3883   $209.39   $209.40   $209.40  
  Purchase #7 $101.92   7.811%   $109.881   $109.88   $109.90   $109.90  
  7 purchase totals = $695.75       $762.7932   $762.80   $762.90   $762.80