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	$89.56	10.751%	$99.1886	$99.19	$99.20	$99.20
Purchase #2	$37.67	5.183%	$39.6224	$39.62	$39.60	$39.60
Purchase #3	$31.51	3.326%	$32.558	$32.56	$32.55	$32.60
Purchase #4	$121.67	3.444%	$125.8603	$125.86	$125.85	$125.90
Purchase #5	$165.42	12.226%	$185.6442	$185.64	$185.65	$185.60
Purchase #6	$98.66	6.487%	$105.0601	$105.06	$105.05	$105.10
Purchase #7	$185.42	11.396%	$206.5505	$206.55	$206.55	$206.60
7 purchase totals =	$729.91		$794.4841	$794.48	$794.45	$794.60