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	$238.82	4.632%	$249.8821	$249.88	$249.90	$249.90
Purchase #2	$89.77	10.592%	$99.2784	$99.28	$99.30	$99.30
Purchase #3	$128.70	9.837%	$141.3602	$141.36	$141.35	$141.40
Purchase #4	$113.95	11.798%	$127.3938	$127.39	$127.40	$127.40
Purchase #5	$245.74	10.332%	$271.1299	$271.13	$271.15	$271.10
Purchase #6	$57.89	8.414%	$62.7609	$62.76	$62.75	$62.80
Purchase #7	$91.35	5.869%	$96.7113	$96.71	$96.70	$96.70
7 purchase totals =	$966.22		$1,048.5166	$1,048.51	$1,048.55	$1,048.60