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	$87.56	3.803%	$90.8899	$90.89	$90.90	$90.90
Purchase #2	$60.47	5.389%	$63.7287	$63.73	$63.75	$63.70
Purchase #3	$207.69	6.289%	$220.7516	$220.75	$220.75	$220.80
Purchase #4	$149.60	11.688%	$167.0852	$167.09	$167.10	$167.10
Purchase #5	$99.34	13.568%	$112.8185	$112.82	$112.80	$112.80
Purchase #6	$185.41	4.309%	$193.3993	$193.40	$193.40	$193.40
Purchase #7	$51.51	8.300%	$55.7853	$55.79	$55.80	$55.80
7 purchase totals =	$841.58		$904.4585	$904.47	$904.50	$904.50