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 $98.87   5.812%   $104.6163   $104.62   $104.60   $104.60  
  Purchase #2 $129.68   3.855%   $134.6792   $134.68   $134.70   $134.70  
  Purchase #3 $172.53   10.651%   $190.9062   $190.91   $190.90   $190.90  
  Purchase #4 $24.98   5.504%   $26.3549   $26.35   $26.35   $26.40  
  Purchase #5 $14.85   13.392%   $16.8387   $16.84   $16.85   $16.80  
  Purchase #6 $140.36   4.498%   $146.6734   $146.67   $146.65   $146.70  
  Purchase #7 $141.58   9.649%   $155.2411   $155.24   $155.25   $155.20  
  7 purchase totals = $722.85       $775.3098   $775.31   $775.30   $775.30