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	$99.71	3.221%	$102.9217	$102.92	$102.90	$102.90
Purchase #2	$189.52	3.836%	$196.79	$196.79	$196.80	$196.80
Purchase #3	$98.96	12.729%	$111.5566	$111.56	$111.55	$111.60
Purchase #4	$229.37	8.185%	$248.1439	$248.14	$248.15	$248.10
Purchase #5	$78.54	3.337%	$81.1609	$81.16	$81.15	$81.20
Purchase #6	$137.76	12.256%	$154.6439	$154.64	$154.65	$154.60
Purchase #7	$112.92	13.832%	$128.5391	$128.54	$128.55	$128.50
7 purchase totals =	$946.78		$1,023.7561	$1,023.75	$1,023.75	$1,023.70