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 $67.83   10.325%   $74.8334   $74.83   $74.85   $74.80  
  Purchase #2 $129.30   5.731%   $136.7102   $136.71   $136.70   $136.70  
  Purchase #3 $25.35   7.115%   $27.1537   $27.15   $27.15   $27.20  
  Purchase #4 $160.93   5.520%   $169.8133   $169.81   $169.80   $169.80  
  Purchase #5 $181.94   9.858%   $199.8756   $199.88   $199.90   $199.90  
  Purchase #6 $186.69   5.359%   $196.6947   $196.69   $196.70   $196.70  
  Purchase #7 $247.66   7.543%   $266.341   $266.34   $266.35   $266.30  
  7 purchase totals = $999.70       $1,071.4219   $1,071.41   $1,071.45   $1,071.40