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 $86.97   10.439%   $96.0488   $96.05   $96.05   $96.00  
  Purchase #2 $99.69   5.390%   $105.0633   $105.06   $105.05   $105.10  
  Purchase #3 $17.85   8.153%   $19.3053   $19.31   $19.30   $19.30  
  Purchase #4 $212.64   4.597%   $222.4151   $222.42   $222.40   $222.40  
  Purchase #5 $164.40   8.230%   $177.9301   $177.93   $177.95   $177.90  
  Purchase #6 $10.46   10.581%   $11.5668   $11.57   $11.55   $11.60  
  Purchase #7 $79.74   6.829%   $85.1854   $85.19   $85.20   $85.20  
  7 purchase totals = $671.75       $717.5148   $717.53   $717.50   $717.50