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	$76.86	13.702%	$87.3914	$87.39	$87.40	$87.40
Purchase #2	$109.40	6.736%	$116.7692	$116.77	$116.75	$116.80
Purchase #3	$154.74	10.755%	$171.3823	$171.38	$171.40	$171.40
Purchase #4	$48.65	13.464%	$55.2002	$55.20	$55.20	$55.20
Purchase #5	$148.92	7.377%	$159.9058	$159.91	$159.90	$159.90
Purchase #6	$121.82	3.369%	$125.9241	$125.92	$125.90	$125.90
Purchase #7	$113.33	4.400%	$118.3165	$118.32	$118.30	$118.30
7 purchase totals =	$773.72		$834.8895	$834.89	$834.85	$834.90