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 $182.93   13.693%   $207.9786   $207.98   $208.00   $208.00  
  Purchase #2 $6.50   12.771%   $7.3301   $7.33   $7.35   $7.30  
  Purchase #3 $177.27   13.288%   $200.8256   $200.83   $200.85   $200.80  
  Purchase #4 $46.73   4.780%   $48.9637   $48.96   $48.95   $49.00  
  Purchase #5 $165.87   8.447%   $179.881   $179.88   $179.90   $179.90  
  Purchase #6 $87.96   7.839%   $94.8552   $94.86   $94.85   $94.90  
  Purchase #7 $24.81   7.430%   $26.6534   $26.65   $26.65   $26.70  
  7 purchase totals = $692.07       $766.4876   $766.49   $766.55   $766.60