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	$227.61	5.563%	$240.2719	$240.27	$240.25	$240.30
Purchase #2	$174.32	9.700%	$191.229	$191.23	$191.25	$191.20
Purchase #3	$193.31	12.324%	$217.1335	$217.13	$217.15	$217.10
Purchase #4	$118.65	8.107%	$128.269	$128.27	$128.25	$128.30
Purchase #5	$51.42	10.630%	$56.8859	$56.89	$56.90	$56.90
Purchase #6	$151.75	12.674%	$170.9828	$170.98	$171.00	$171.00
Purchase #7	$57.25	3.614%	$59.319	$59.32	$59.30	$59.30
7 purchase totals =	$974.31		$1,064.0911	$1,064.09	$1,064.10	$1,064.10