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 $71.49   7.107%   $76.5708   $76.57   $76.55   $76.60  
  Purchase #2 $87.37   6.742%   $93.2605   $93.26   $93.25   $93.30  
  Purchase #3 $86.84   13.452%   $98.5217   $98.52   $98.50   $98.50  
  Purchase #4 $178.82   6.677%   $190.7598   $190.76   $190.75   $190.80  
  Purchase #5 $53.70   8.537%   $58.2844   $58.28   $58.30   $58.30  
  Purchase #6 $87.80   6.544%   $93.5456   $93.55   $93.55   $93.50  
  Purchase #7 $124.39   5.405%   $131.1133   $131.11   $131.10   $131.10  
  7 purchase totals = $690.41       $742.0561   $742.05   $742.00   $742.10