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	$91.99	8.407%	$99.7236	$99.72	$99.70	$99.70
Purchase #2	$85.78	4.669%	$89.7851	$89.79	$89.80	$89.80
Purchase #3	$166.40	13.578%	$188.9938	$188.99	$189.00	$189.00
Purchase #4	$185.39	7.590%	$199.4611	$199.46	$199.45	$199.50
Purchase #5	$159.66	7.481%	$171.6042	$171.60	$171.60	$171.60
Purchase #6	$68.53	12.180%	$76.877	$76.88	$76.90	$76.90
Purchase #7	$176.89	8.662%	$192.2122	$192.21	$192.20	$192.20
7 purchase totals =	$934.64		$1,018.6570	$1,018.65	$1,018.65	$1,018.70