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	$69.28	5.244%	$72.913	$72.91	$72.90	$72.90
Purchase #2	$111.73	6.433%	$118.9176	$118.92	$118.90	$118.90
Purchase #3	$100.36	9.318%	$109.7115	$109.71	$109.70	$109.70
Purchase #4	$39.54	3.648%	$40.9824	$40.98	$41.00	$41.00
Purchase #5	$43.89	3.172%	$45.2822	$45.28	$45.30	$45.30
Purchase #6	$192.29	7.302%	$206.331	$206.33	$206.35	$206.30
Purchase #7	$37.77	11.229%	$42.0112	$42.01	$42.00	$42.00
7 purchase totals =	$594.86		$636.1489	$636.14	$636.15	$636.10