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 $149.69   10.249%   $165.0317   $165.03   $165.05   $165.00  
  Purchase #2 $222.88   11.361%   $248.2014   $248.20   $248.20   $248.20  
  Purchase #3 $66.52   4.586%   $69.5706   $69.57   $69.55   $69.60  
  Purchase #4 $218.55   10.398%   $241.2748   $241.27   $241.25   $241.30  
  Purchase #5 $87.25   7.463%   $93.7615   $93.76   $93.75   $93.80  
  Purchase #6 $79.97   9.864%   $87.8582   $87.86   $87.85   $87.90  
  Purchase #7 $52.88   8.374%   $57.3082   $57.31   $57.30   $57.30  
  7 purchase totals = $877.74       $963.0064   $963.00   $962.95   $963.10