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 $144.99   7.246%   $155.496   $155.50   $155.50   $155.50  
  Purchase #2 $250.69   13.304%   $284.0418   $284.04   $284.05   $284.00  
  Purchase #3 $26.83   13.734%   $30.5148   $30.51   $30.50   $30.50  
  Purchase #4 $175.45   12.418%   $197.2374   $197.24   $197.25   $197.20  
  Purchase #5 $159.96   11.414%   $178.2178   $178.22   $178.20   $178.20  
  Purchase #6 $105.55   7.255%   $113.2077   $113.21   $113.20   $113.20  
  Purchase #7 $89.62   13.272%   $101.5144   $101.51   $101.50   $101.50  
  7 purchase totals = $953.09       $1,060.2299   $1,060.23   $1,060.20   $1,060.10