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 $226.85   5.372%   $239.0364   $239.04   $239.05   $239.00  
  Purchase #2 $17.72   4.609%   $18.5367   $18.54   $18.55   $18.50  
  Purchase #3 $57.71   12.349%   $64.8366   $64.84   $64.85   $64.80  
  Purchase #4 $184.81   13.116%   $209.0497   $209.05   $209.05   $209.00  
  Purchase #5 $153.80   7.243%   $164.9397   $164.94   $164.95   $164.90  
  Purchase #6 $164.53   5.370%   $173.3653   $173.37   $173.35   $173.40  
  Purchase #7 $55.81   4.658%   $58.4096   $58.41   $58.40   $58.40  
  7 purchase totals = $861.23       $928.1740   $928.19   $928.20   $928.00