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	$159.93	4.363%	$166.9077	$166.91	$166.90	$166.90
Purchase #2	$43.66	5.317%	$45.9814	$45.98	$46.00	$46.00
Purchase #3	$49.36	9.873%	$54.2333	$54.23	$54.25	$54.20
Purchase #4	$133.47	7.180%	$143.0531	$143.05	$143.05	$143.10
Purchase #5	$76.76	4.668%	$80.3432	$80.34	$80.35	$80.30
Purchase #6	$99.43	11.776%	$111.1389	$111.14	$111.15	$111.10
Purchase #7	$201.59	3.785%	$209.2202	$209.22	$209.20	$209.20
7 purchase totals =	$764.20		$810.8778	$810.87	$810.90	$810.80