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 $54.38   13.403%   $61.6686   $61.67   $61.65   $61.70  
  Purchase #2 $202.75   5.566%   $214.0351   $214.04   $214.05   $214.00  
  Purchase #3 $179.73   9.821%   $197.3813   $197.38   $197.40   $197.40  
  Purchase #4 $169.69   5.802%   $179.5354   $179.54   $179.55   $179.50  
  Purchase #5 $164.62   8.631%   $178.8284   $178.83   $178.85   $178.80  
  Purchase #6 $185.43   8.123%   $200.4925   $200.49   $200.50   $200.50  
  Purchase #7 $101.82   13.229%   $115.2898   $115.29   $115.30   $115.30  
  7 purchase totals = $1,058.42       $1,147.2311   $1,147.24   $1,147.30   $1,147.20