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 $79.58   9.104%   $86.825   $86.83   $86.85   $86.80  
  Purchase #2 $161.32   4.772%   $169.0182   $169.02   $169.00   $169.00  
  Purchase #3 $72.27   10.369%   $79.7637   $79.76   $79.75   $79.80  
  Purchase #4 $218.28   12.823%   $246.27   $246.27   $246.25   $246.30  
  Purchase #5 $53.37   4.823%   $55.944   $55.94   $55.95   $55.90  
  Purchase #6 $91.85   13.522%   $104.27   $104.27   $104.25   $104.30  
  Purchase #7 $152.80   12.377%   $171.7121   $171.71   $171.70   $171.70  
  7 purchase totals = $829.47       $913.8030   $913.80   $913.75   $913.80