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	$227.84	4.611%	$238.3457	$238.35	$238.35	$238.30
Purchase #2	$83.70	8.300%	$90.6471	$90.65	$90.65	$90.60
Purchase #3	$79.41	12.676%	$89.476	$89.48	$89.50	$89.50
Purchase #4	$121.33	3.556%	$125.6445	$125.64	$125.65	$125.60
Purchase #5	$131.90	3.740%	$136.8331	$136.83	$136.85	$136.80
Purchase #6	$48.72	8.565%	$52.8929	$52.89	$52.90	$52.90
Purchase #7	$155.39	11.622%	$173.4494	$173.45	$173.45	$173.40
7 purchase totals =	$848.29		$907.2887	$907.29	$907.35	$907.10