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 $134.87   10.626%   $149.2013   $149.20   $149.20   $149.20  
  Purchase #2 $185.89   13.787%   $211.5187   $211.52   $211.50   $211.50  
  Purchase #3 $33.60   13.703%   $38.2042   $38.20   $38.20   $38.20  
  Purchase #4 $121.63   10.153%   $133.9791   $133.98   $134.00   $134.00  
  Purchase #5 $56.81   10.446%   $62.7444   $62.74   $62.75   $62.70  
  Purchase #6 $195.88   9.244%   $213.9871   $213.99   $214.00   $214.00  
  Purchase #7 $22.44   5.404%   $23.6527   $23.65   $23.65   $23.70  
  7 purchase totals = $751.12       $833.2875   $833.28   $833.30   $833.30