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 $69.39   5.662%   $73.3189   $73.32   $73.30   $73.30  
  Purchase #2 $100.75   3.291%   $104.0657   $104.07   $104.05   $104.10  
  Purchase #3 $50.58   5.594%   $53.4094   $53.41   $53.40   $53.40  
  Purchase #4 $68.34   12.516%   $76.8934   $76.89   $76.90   $76.90  
  Purchase #5 $69.58   13.821%   $79.1967   $79.20   $79.20   $79.20  
  Purchase #6 $88.54   5.641%   $93.5345   $93.53   $93.55   $93.50  
  Purchase #7 $29.64   6.541%   $31.5788   $31.58   $31.60   $31.60  
  7 purchase totals = $476.82       $511.9974   $512.00   $512.00   $512.00