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 $213.99   10.734%   $236.9597   $236.96   $236.95   $237.00  
  Purchase #2 $59.27   13.566%   $67.3106   $67.31   $67.30   $67.30  
  Purchase #3 $83.60   3.125%   $86.2125   $86.21   $86.20   $86.20  
  Purchase #4 $145.44   13.803%   $165.5151   $165.52   $165.50   $165.50  
  Purchase #5 $194.67   3.257%   $201.0104   $201.01   $201.00   $201.00  
  Purchase #6 $50.84   8.630%   $55.2275   $55.23   $55.25   $55.20  
  Purchase #7 $182.45   5.241%   $192.0122   $192.01   $192.00   $192.00  
  7 purchase totals = $930.26       $1,004.2480   $1,004.25   $1,004.20   $1,004.20