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 $34.98   10.238%   $38.5613   $38.56   $38.55   $38.60  
  Purchase #2 $224.34   4.546%   $234.5385   $234.54   $234.55   $234.50  
  Purchase #3 $70.59   9.562%   $77.3398   $77.34   $77.35   $77.30  
  Purchase #4 $217.81   7.349%   $233.8169   $233.82   $233.80   $233.80  
  Purchase #5 $54.82   3.860%   $56.9361   $56.94   $56.95   $56.90  
  Purchase #6 $136.90   12.461%   $153.9591   $153.96   $153.95   $154.00  
  Purchase #7 $123.60   5.731%   $130.6835   $130.68   $130.70   $130.70  
  7 purchase totals = $863.04       $925.8352   $925.84   $925.85   $925.80