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	$75.73	3.798%	$78.6062	$78.61	$78.60	$78.60
Purchase #2	$57.37	11.834%	$64.1592	$64.16	$64.15	$64.20
Purchase #3	$91.32	11.452%	$101.778	$101.78	$101.80	$101.80
Purchase #4	$79.68	9.610%	$87.3372	$87.34	$87.35	$87.30
Purchase #5	$93.56	4.258%	$97.5438	$97.54	$97.55	$97.50
Purchase #6	$127.56	3.384%	$131.8766	$131.88	$131.90	$131.90
Purchase #7	$101.98	7.255%	$109.3786	$109.38	$109.40	$109.40
7 purchase totals =	$627.20		$670.6796	$670.69	$670.75	$670.70