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	$73.82	4.182%	$76.9072	$76.91	$76.90	$76.90
Purchase #2	$123.43	3.230%	$127.4168	$127.42	$127.40	$127.40
Purchase #3	$240.46	5.206%	$252.9783	$252.98	$253.00	$253.00
Purchase #4	$96.26	3.717%	$99.838	$99.84	$99.85	$99.80
Purchase #5	$218.44	11.316%	$243.1587	$243.16	$243.15	$243.20
Purchase #6	$246.59	5.327%	$259.7258	$259.73	$259.75	$259.70
Purchase #7	$38.38	4.773%	$40.2119	$40.21	$40.20	$40.20
7 purchase totals =	$1,037.38		$1,100.2367	$1,100.25	$1,100.25	$1,100.20