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	$91.83	8.375%	$99.5208	$99.52	$99.50	$99.50
Purchase #2	$159.97	7.449%	$171.8862	$171.89	$171.90	$171.90
Purchase #3	$33.96	12.675%	$38.2644	$38.26	$38.25	$38.30
Purchase #4	$96.92	13.584%	$110.0856	$110.09	$110.10	$110.10
Purchase #5	$126.48	12.391%	$142.1521	$142.15	$142.15	$142.20
Purchase #6	$89.80	11.317%	$99.9627	$99.96	$99.95	$100.00
Purchase #7	$125.53	13.787%	$142.8368	$142.84	$142.85	$142.80
7 purchase totals =	$724.49		$804.7086	$804.71	$804.70	$804.80