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 $64.53   13.545%   $73.2706   $73.27   $73.25   $73.30  
  Purchase #2 $86.40   9.342%   $94.4715   $94.47   $94.45   $94.50  
  Purchase #3 $44.96   10.531%   $49.6947   $49.69   $49.70   $49.70  
  Purchase #4 $65.37   8.331%   $70.816   $70.82   $70.80   $70.80  
  Purchase #5 $214.65   3.231%   $221.5853   $221.59   $221.60   $221.60  
  Purchase #6 $169.89   7.520%   $182.6657   $182.67   $182.65   $182.70  
  Purchase #7 $87.29   7.489%   $93.8271   $93.83   $93.85   $93.80  
  7 purchase totals = $733.09       $786.3309   $786.34   $786.30   $786.40