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	$132.32	3.385%	$136.799	$136.80	$136.80	$136.80
Purchase #2	$210.71	11.121%	$234.1431	$234.14	$234.15	$234.10
Purchase #3	$97.79	13.103%	$110.6034	$110.60	$110.60	$110.60
Purchase #4	$80.85	6.236%	$85.8918	$85.89	$85.90	$85.90
Purchase #5	$30.78	6.290%	$32.7161	$32.72	$32.70	$32.70
Purchase #6	$79.32	3.827%	$82.3556	$82.36	$82.35	$82.40
Purchase #7	$54.27	8.547%	$58.9085	$58.91	$58.90	$58.90
7 purchase totals =	$686.04		$741.4175	$741.42	$741.40	$741.40