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 $11.82   4.506%   $12.3526   $12.35   $12.35   $12.40  
  Purchase #2 $31.85   12.808%   $35.9293   $35.93   $35.95   $35.90  
  Purchase #3 $248.95   7.201%   $266.8769   $266.88   $266.90   $266.90  
  Purchase #4 $43.63   6.491%   $46.462   $46.46   $46.45   $46.50  
  Purchase #5 $246.88   6.787%   $263.6357   $263.64   $263.65   $263.60  
  Purchase #6 $156.39   6.574%   $166.6711   $166.67   $166.65   $166.70  
  Purchase #7 $187.48   4.571%   $196.0497   $196.05   $196.05   $196.00  
  7 purchase totals = $927.00       $987.9773   $987.98   $988.00   $988.00