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 $205.35   12.756%   $231.5444   $231.54   $231.55   $231.50  
  Purchase #2 $14.27   6.510%   $15.199   $15.20   $15.20   $15.20  
  Purchase #3 $216.63   3.761%   $224.7775   $224.78   $224.80   $224.80  
  Purchase #4 $238.90   13.694%   $271.615   $271.62   $271.60   $271.60  
  Purchase #5 $177.43   7.514%   $190.7621   $190.76   $190.75   $190.80  
  Purchase #6 $43.33   10.177%   $47.7397   $47.74   $47.75   $47.70  
  Purchase #7 $39.94   11.610%   $44.577   $44.58   $44.60   $44.60  
  7 purchase totals = $935.85       $1,026.2147   $1,026.22   $1,026.25   $1,026.20