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	$229.28	12.120%	$257.0687	$257.07	$257.05	$257.10
Purchase #2	$243.54	5.413%	$256.7228	$256.72	$256.70	$256.70
Purchase #3	$57.74	6.220%	$61.3314	$61.33	$61.35	$61.30
Purchase #4	$231.76	13.190%	$262.3291	$262.33	$262.35	$262.30
Purchase #5	$81.53	12.408%	$91.6462	$91.65	$91.65	$91.60
Purchase #6	$141.85	4.391%	$148.0786	$148.08	$148.10	$148.10
Purchase #7	$70.96	10.276%	$78.2518	$78.25	$78.25	$78.30
7 purchase totals =	$1,056.66		$1,155.4286	$1,155.43	$1,155.45	$1,155.40