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 $236.35   9.637%   $259.127   $259.13   $259.15   $259.10  
  Purchase #2 $60.92   13.786%   $69.3184   $69.32   $69.30   $69.30  
  Purchase #3 $115.36   4.175%   $120.1763   $120.18   $120.20   $120.20  
  Purchase #4 $148.47   12.842%   $167.5365   $167.54   $167.55   $167.50  
  Purchase #5 $223.51   10.404%   $246.764   $246.76   $246.75   $246.80  
  Purchase #6 $77.64   3.423%   $80.2976   $80.30   $80.30   $80.30  
  Purchase #7 $24.85   6.607%   $26.4918   $26.49   $26.50   $26.50  
  7 purchase totals = $887.10       $969.7116   $969.72   $969.75   $969.70