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	$161.56	5.163%	$169.9013	$169.90	$169.90	$169.90
Purchase #2	$241.93	9.326%	$264.4924	$264.49	$264.50	$264.50
Purchase #3	$69.56	11.283%	$77.4085	$77.41	$77.40	$77.40
Purchase #4	$158.30	8.613%	$171.9344	$171.93	$171.95	$171.90
Purchase #5	$211.33	8.700%	$229.7157	$229.72	$229.70	$229.70
Purchase #6	$98.57	13.210%	$111.5911	$111.59	$111.60	$111.60
Purchase #7	$237.76	3.185%	$245.3327	$245.33	$245.35	$245.30
7 purchase totals =	$1,179.01		$1,270.3761	$1,270.37	$1,270.40	$1,270.30