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	$209.40	4.505%	$218.8335	$218.83	$218.85	$218.80
Purchase #2	$137.55	8.180%	$148.8016	$148.80	$148.80	$148.80
Purchase #3	$65.66	8.266%	$71.0875	$71.09	$71.10	$71.10
Purchase #4	$40.34	11.288%	$44.8936	$44.89	$44.90	$44.90
Purchase #5	$75.99	3.649%	$78.7629	$78.76	$78.75	$78.80
Purchase #6	$160.32	6.234%	$170.3143	$170.31	$170.30	$170.30
Purchase #7	$74.72	10.237%	$82.3691	$82.37	$82.35	$82.40
7 purchase totals =	$763.98		$815.0625	$815.05	$815.05	$815.10