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 $61.64   12.141%   $69.1237   $69.12   $69.10   $69.10  
  Purchase #2 $97.35   6.655%   $103.8286   $103.83   $103.85   $103.80  
  Purchase #3 $48.76   9.291%   $53.2903   $53.29   $53.30   $53.30  
  Purchase #4 $166.57   12.797%   $187.886   $187.89   $187.90   $187.90  
  Purchase #5 $153.25   10.764%   $169.7458   $169.75   $169.75   $169.70  
  Purchase #6 $66.76   4.589%   $69.8236   $69.82   $69.80   $69.80  
  Purchase #7 $56.66   10.443%   $62.577   $62.58   $62.60   $62.60  
  7 purchase totals = $650.99       $716.2750   $716.28   $716.30   $716.20