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 $60.80   5.722%   $64.279   $64.28   $64.30   $64.30  
  Purchase #2 $87.31   9.622%   $95.711   $95.71   $95.70   $95.70  
  Purchase #3 $177.52   8.509%   $192.6252   $192.63   $192.65   $192.60  
  Purchase #4 $134.98   5.638%   $142.5902   $142.59   $142.60   $142.60  
  Purchase #5 $67.46   5.486%   $71.1609   $71.16   $71.15   $71.20  
  Purchase #6 $229.56   13.221%   $259.9101   $259.91   $259.90   $259.90  
  Purchase #7 $8.94   10.738%   $9.9   $9.90   $9.90   $9.90  
  7 purchase totals = $766.57       $836.1764   $836.18   $836.20   $836.20