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	$65.55	10.275%	$72.2853	$72.29	$72.30	$72.30
Purchase #2	$163.97	3.502%	$169.7122	$169.71	$169.70	$169.70
Purchase #3	$122.73	8.280%	$132.892	$132.89	$132.90	$132.90
Purchase #4	$143.40	9.365%	$156.8294	$156.83	$156.85	$156.80
Purchase #5	$226.65	6.224%	$240.7567	$240.76	$240.75	$240.80
Purchase #6	$136.71	13.580%	$155.2752	$155.28	$155.30	$155.30
Purchase #7	$146.96	10.593%	$162.5275	$162.53	$162.55	$162.50
7 purchase totals =	$1,005.97		$1,090.2783	$1,090.29	$1,090.35	$1,090.30