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	$83.73	4.266%	$87.3019	$87.30	$87.30	$87.30
Purchase #2	$111.92	11.254%	$124.5155	$124.52	$124.50	$124.50
Purchase #3	$37.52	12.680%	$42.2775	$42.28	$42.30	$42.30
Purchase #4	$30.87	9.135%	$33.69	$33.69	$33.70	$33.70
Purchase #5	$67.79	8.755%	$73.725	$73.73	$73.75	$73.70
Purchase #6	$162.64	5.466%	$171.5299	$171.53	$171.55	$171.50
Purchase #7	$16.58	13.269%	$18.78	$18.78	$18.80	$18.80
7 purchase totals =	$511.05		$551.8198	$551.83	$551.90	$551.80