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	$30.76	3.173%	$31.736	$31.74	$31.75	$31.70
Purchase #2	$185.62	13.507%	$210.6917	$210.69	$210.70	$210.70
Purchase #3	$97.50	8.154%	$105.4502	$105.45	$105.45	$105.50
Purchase #4	$223.54	6.516%	$238.1059	$238.11	$238.10	$238.10
Purchase #5	$189.77	5.822%	$200.8184	$200.82	$200.80	$200.80
Purchase #6	$29.77	3.334%	$30.7625	$30.76	$30.75	$30.80
Purchase #7	$205.59	9.579%	$225.2835	$225.28	$225.30	$225.30
7 purchase totals =	$962.55		$1,042.8482	$1,042.85	$1,042.85	$1,042.90