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 $245.58   8.713%   $266.9774   $266.98   $267.00   $267.00  
  Purchase #2 $156.83   5.865%   $166.0281   $166.03   $166.05   $166.00  
  Purchase #3 $68.86   12.685%   $77.5949   $77.59   $77.60   $77.60  
  Purchase #4 $102.81   10.819%   $113.933   $113.93   $113.95   $113.90  
  Purchase #5 $67.29   8.566%   $73.0541   $73.05   $73.05   $73.10  
  Purchase #6 $36.88   8.639%   $40.0661   $40.07   $40.05   $40.10  
  Purchase #7 $239.83   3.447%   $248.0969   $248.10   $248.10   $248.10  
  7 purchase totals = $918.08       $985.7505   $985.75   $985.80   $985.80