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 $52.90   7.485%   $56.8596   $56.86   $56.85   $56.90  
  Purchase #2 $222.46   5.337%   $234.3327   $234.33   $234.35   $234.30  
  Purchase #3 $29.95   8.325%   $32.4433   $32.44   $32.45   $32.40  
  Purchase #4 $198.38   5.224%   $208.7434   $208.74   $208.75   $208.70  
  Purchase #5 $216.94   12.641%   $244.3634   $244.36   $244.35   $244.40  
  Purchase #6 $175.72   8.689%   $190.9883   $190.99   $191.00   $191.00  
  Purchase #7 $38.87   12.845%   $43.8629   $43.86   $43.85   $43.90  
  7 purchase totals = $935.22       $1,011.5936   $1,011.58   $1,011.60   $1,011.60