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 $60.91   13.399%   $69.0713   $69.07   $69.05   $69.10  
  Purchase #2 $97.96   13.752%   $111.4315   $111.43   $111.45   $111.40  
  Purchase #3 $67.46   6.841%   $72.0749   $72.07   $72.05   $72.10  
  Purchase #4 $47.65   4.408%   $49.7504   $49.75   $49.75   $49.80  
  Purchase #5 $214.27   11.735%   $239.4146   $239.41   $239.40   $239.40  
  Purchase #6 $235.65   5.138%   $247.7577   $247.76   $247.75   $247.80  
  Purchase #7 $51.63   9.136%   $56.3469   $56.35   $56.35   $56.30  
  7 purchase totals = $775.53       $845.8473   $845.84   $845.80   $845.90