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 $217.50   11.822%   $243.2129   $243.21   $243.20   $243.20  
  Purchase #2 $52.83   11.605%   $58.9609   $58.96   $58.95   $59.00  
  Purchase #3 $140.58   8.304%   $152.2538   $152.25   $152.25   $152.30  
  Purchase #4 $171.67   13.509%   $194.8609   $194.86   $194.85   $194.90  
  Purchase #5 $186.33   4.724%   $195.1322   $195.13   $195.15   $195.10  
  Purchase #6 $182.99   12.776%   $206.3688   $206.37   $206.35   $206.40  
  Purchase #7 $149.56   4.110%   $155.7069   $155.71   $155.70   $155.70  
  7 purchase totals = $1,101.46       $1,206.4964   $1,206.49   $1,206.45   $1,206.60