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	$40.67	11.692%	$45.4251	$45.43	$45.45	$45.40
Purchase #2	$235.81	12.345%	$264.9207	$264.92	$264.90	$264.90
Purchase #3	$40.51	3.451%	$41.908	$41.91	$41.90	$41.90
Purchase #4	$174.47	3.102%	$179.8821	$179.88	$179.90	$179.90
Purchase #5	$31.88	11.588%	$35.5743	$35.57	$35.55	$35.60
Purchase #6	$101.32	3.467%	$104.8328	$104.83	$104.85	$104.80
Purchase #7	$131.44	6.326%	$139.7549	$139.75	$139.75	$139.80
7 purchase totals =	$756.10		$812.2979	$812.29	$812.30	$812.30