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 $195.50   11.861%   $218.6883   $218.69   $218.70   $218.70  
  Purchase #2 $77.91   13.324%   $88.2907   $88.29   $88.30   $88.30  
  Purchase #3 $111.34   11.361%   $123.9893   $123.99   $124.00   $124.00  
  Purchase #4 $80.49   13.423%   $91.2942   $91.29   $91.30   $91.30  
  Purchase #5 $131.74   4.144%   $137.1993   $137.20   $137.20   $137.20  
  Purchase #6 $41.90   4.344%   $43.7201   $43.72   $43.70   $43.70  
  Purchase #7 $26.53   9.506%   $29.0519   $29.05   $29.05   $29.10  
  7 purchase totals = $665.41       $732.2338   $732.23   $732.25   $732.30