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 $80.66   13.632%   $91.6556   $91.66   $91.65   $91.70  
  Purchase #2 $53.68   9.228%   $58.6336   $58.63   $58.65   $58.60  
  Purchase #3 $53.68   8.602%   $58.2976   $58.30   $58.30   $58.30  
  Purchase #4 $250.74   9.312%   $274.0889   $274.09   $274.10   $274.10  
  Purchase #5 $235.43   6.340%   $250.3563   $250.36   $250.35   $250.40  
  Purchase #6 $152.47   12.253%   $171.1521   $171.15   $171.15   $171.20  
  Purchase #7 $49.33   12.607%   $55.549   $55.55   $55.55   $55.50  
  7 purchase totals = $875.99       $959.7331   $959.74   $959.75   $959.80