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	$88.58	12.800%	$99.9182	$99.92	$99.90	$99.90
Purchase #2	$156.58	13.773%	$178.1458	$178.15	$178.15	$178.10
Purchase #3	$155.40	12.708%	$175.1482	$175.15	$175.15	$175.10
Purchase #4	$234.41	13.187%	$265.3216	$265.32	$265.30	$265.30
Purchase #5	$35.54	7.735%	$38.289	$38.29	$38.30	$38.30
Purchase #6	$47.36	6.707%	$50.5364	$50.54	$50.55	$50.50
Purchase #7	$159.37	4.718%	$166.8891	$166.89	$166.90	$166.90
7 purchase totals =	$877.24		$974.2483	$974.26	$974.25	$974.10