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 $217.79   10.207%   $240.0198   $240.02   $240.00   $240.00  
  Purchase #2 $178.33   10.434%   $196.937   $196.94   $196.95   $196.90  
  Purchase #3 $237.87   3.414%   $245.9909   $245.99   $246.00   $246.00  
  Purchase #4 $61.69   11.317%   $68.6715   $68.67   $68.65   $68.70  
  Purchase #5 $180.59   3.334%   $186.6109   $186.61   $186.60   $186.60  
  Purchase #6 $242.34   9.305%   $264.8897   $264.89   $264.90   $264.90  
  Purchase #7 $206.63   7.270%   $221.652   $221.65   $221.65   $221.70  
  7 purchase totals = $1,325.24       $1,424.7718   $1,424.77   $1,424.75   $1,424.80