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	$158.58	12.737%	$178.7783	$178.78	$178.80	$178.80
Purchase #2	$128.26	10.288%	$141.4554	$141.46	$141.45	$141.50
Purchase #3	$84.58	4.598%	$88.469	$88.47	$88.45	$88.50
Purchase #4	$36.88	9.240%	$40.2877	$40.29	$40.30	$40.30
Purchase #5	$5.90	10.814%	$6.538	$6.54	$6.55	$6.50
Purchase #6	$234.45	12.323%	$263.3413	$263.34	$263.35	$263.30
Purchase #7	$103.52	10.380%	$114.2654	$114.27	$114.25	$114.30
7 purchase totals =	$752.17		$833.1351	$833.15	$833.15	$833.20