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	$236.76	3.385%	$244.7743	$244.77	$244.75	$244.80
Purchase #2	$16.74	9.637%	$18.3532	$18.35	$18.35	$18.40
Purchase #3	$201.32	12.813%	$227.1151	$227.12	$227.10	$227.10
Purchase #4	$24.92	13.872%	$28.3769	$28.38	$28.40	$28.40
Purchase #5	$79.42	12.492%	$89.3411	$89.34	$89.35	$89.30
Purchase #6	$82.92	6.422%	$88.2451	$88.25	$88.25	$88.20
Purchase #7	$69.59	13.207%	$78.7808	$78.78	$78.80	$78.80
7 purchase totals =	$711.67		$774.9865	$774.99	$775.00	$775.00