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	$23.57	3.770%	$24.4586	$24.46	$24.45	$24.50
Purchase #2	$55.83	4.561%	$58.3764	$58.38	$58.40	$58.40
Purchase #3	$25.51	9.103%	$27.8322	$27.83	$27.85	$27.80
Purchase #4	$86.73	3.256%	$89.5539	$89.55	$89.55	$89.60
Purchase #5	$72.29	11.864%	$80.8665	$80.87	$80.85	$80.90
Purchase #6	$43.54	9.773%	$47.7952	$47.80	$47.80	$47.80
Purchase #7	$112.86	11.559%	$125.9055	$125.91	$125.90	$125.90
7 purchase totals =	$420.33		$454.7883	$454.80	$454.80	$454.90