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 $77.36   10.679%   $85.6213   $85.62   $85.60   $85.60  
  Purchase #2 $54.91   8.706%   $59.6905   $59.69   $59.70   $59.70  
  Purchase #3 $120.69   10.701%   $133.605   $133.61   $133.60   $133.60  
  Purchase #4 $36.51   5.170%   $38.3976   $38.40   $38.40   $38.40  
  Purchase #5 $222.63   3.596%   $230.6358   $230.64   $230.65   $230.60  
  Purchase #6 $129.80   4.187%   $135.2347   $135.23   $135.25   $135.20  
  Purchase #7 $77.35   5.652%   $81.7218   $81.72   $81.70   $81.70  
  7 purchase totals = $719.25       $764.9067   $764.91   $764.90   $764.80