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 $76.52   8.873%   $83.3096   $83.31   $83.30   $83.30  
  Purchase #2 $68.74   11.461%   $76.6183   $76.62   $76.60   $76.60  
  Purchase #3 $154.73   5.146%   $162.6924   $162.69   $162.70   $162.70  
  Purchase #4 $168.25   5.573%   $177.6266   $177.63   $177.65   $177.60  
  Purchase #5 $109.99   7.813%   $118.5835   $118.58   $118.60   $118.60  
  Purchase #6 $8.52   6.771%   $9.0969   $9.10   $9.10   $9.10  
  Purchase #7 $104.71   10.809%   $116.0281   $116.03   $116.05   $116.00  
  7 purchase totals = $691.46       $743.9554   $743.96   $744.00   $743.90