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	$247.71	6.218%	$263.1126	$263.11	$263.10	$263.10
Purchase #2	$56.32	9.748%	$61.8101	$61.81	$61.80	$61.80
Purchase #3	$245.33	6.167%	$260.4595	$260.46	$260.45	$260.50
Purchase #4	$100.80	9.504%	$110.38	$110.38	$110.40	$110.40
Purchase #5	$112.32	13.813%	$127.8348	$127.83	$127.85	$127.80
Purchase #6	$96.49	13.833%	$109.8375	$109.84	$109.85	$109.80
Purchase #7	$57.32	9.698%	$62.8789	$62.88	$62.90	$62.90
7 purchase totals =	$916.29		$996.3134	$996.31	$996.35	$996.30