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 $40.35   8.671%   $43.8487   $43.85   $43.85   $43.80  
  Purchase #2 $220.89   3.383%   $228.3627   $228.36   $228.35   $228.40  
  Purchase #3 $22.63   12.621%   $25.4861   $25.49   $25.50   $25.50  
  Purchase #4 $234.91   4.713%   $245.9813   $245.98   $246.00   $246.00  
  Purchase #5 $43.25   8.140%   $46.7706   $46.77   $46.75   $46.80  
  Purchase #6 $215.60   9.683%   $236.4765   $236.48   $236.50   $236.50  
  Purchase #7 $183.73   8.813%   $199.9221   $199.92   $199.90   $199.90  
  7 purchase totals = $961.36       $1,026.8480   $1,026.85   $1,026.85   $1,026.90