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 $91.34   11.589%   $101.9254   $101.93   $101.95   $101.90  
  Purchase #2 $13.58   4.692%   $14.2172   $14.22   $14.20   $14.20  
  Purchase #3 $61.27   13.798%   $69.724   $69.72   $69.70   $69.70  
  Purchase #4 $226.48   4.592%   $236.88   $236.88   $236.90   $236.90  
  Purchase #5 $157.85   4.789%   $165.4094   $165.41   $165.40   $165.40  
  Purchase #6 $5.85   5.361%   $6.1636   $6.16   $6.15   $6.20  
  Purchase #7 $63.38   11.819%   $70.8709   $70.87   $70.85   $70.90  
  7 purchase totals = $619.75       $665.1905   $665.19   $665.15   $665.20