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 $164.47   8.730%   $178.8282   $178.83   $178.85   $178.80  
  Purchase #2 $246.26   8.639%   $267.5344   $267.53   $267.55   $267.50  
  Purchase #3 $226.79   6.489%   $241.5064   $241.51   $241.50   $241.50  
  Purchase #4 $108.27   13.451%   $122.8334   $122.83   $122.85   $122.80  
  Purchase #5 $173.67   13.322%   $196.8063   $196.81   $196.80   $196.80  
  Purchase #6 $76.75   11.127%   $85.29   $85.29   $85.30   $85.30  
  Purchase #7 $129.92   9.813%   $142.669   $142.67   $142.65   $142.70  
  7 purchase totals = $1,126.13       $1,235.4677   $1,235.47   $1,235.50   $1,235.40