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	$231.27	6.832%	$247.0704	$247.07	$247.05	$247.10
Purchase #2	$165.55	13.791%	$188.381	$188.38	$188.40	$188.40
Purchase #3	$40.82	6.736%	$43.5696	$43.57	$43.55	$43.60
Purchase #4	$99.62	8.483%	$108.0708	$108.07	$108.05	$108.10
Purchase #5	$132.92	7.299%	$142.6218	$142.62	$142.60	$142.60
Purchase #6	$57.89	8.689%	$62.9201	$62.92	$62.90	$62.90
Purchase #7	$98.91	11.804%	$110.5853	$110.59	$110.60	$110.60
7 purchase totals =	$826.98		$903.2190	$903.22	$903.15	$903.30