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 $34.59   8.665%   $37.5872   $37.59   $37.60   $37.60  
  Purchase #2 $64.27   4.722%   $67.3048   $67.30   $67.30   $67.30  
  Purchase #3 $13.66   6.463%   $14.5428   $14.54   $14.55   $14.50  
  Purchase #4 $122.42   11.303%   $136.2571   $136.26   $136.25   $136.30  
  Purchase #5 $231.87   5.129%   $243.7626   $243.76   $243.75   $243.80  
  Purchase #6 $49.87   3.411%   $51.5711   $51.57   $51.55   $51.60  
  Purchase #7 $118.50   6.338%   $126.0105   $126.01   $126.00   $126.00  
  7 purchase totals = $635.18       $677.0361   $677.03   $677.00   $677.10