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 $192.86   9.629%   $211.4305   $211.43   $211.45   $211.40  
  Purchase #2 $154.32   10.609%   $170.6918   $170.69   $170.70   $170.70  
  Purchase #3 $60.28   11.402%   $67.1531   $67.15   $67.15   $67.20  
  Purchase #4 $188.93   9.403%   $206.6951   $206.70   $206.70   $206.70  
  Purchase #5 $144.48   6.795%   $154.2974   $154.30   $154.30   $154.30  
  Purchase #6 $101.96   11.674%   $113.8628   $113.86   $113.85   $113.90  
  Purchase #7 $91.97   8.649%   $99.9245   $99.92   $99.90   $99.90  
  7 purchase totals = $934.80       $1,024.0552   $1,024.05   $1,024.05   $1,024.10