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	$250.71	13.854%	$285.4434	$285.44	$285.45	$285.40
Purchase #2	$64.64	10.654%	$71.5267	$71.53	$71.55	$71.50
Purchase #3	$86.53	13.129%	$97.8905	$97.89	$97.90	$97.90
Purchase #4	$16.70	9.375%	$18.2656	$18.27	$18.25	$18.30
Purchase #5	$89.31	12.392%	$100.3773	$100.38	$100.40	$100.40
Purchase #6	$138.48	9.502%	$151.6384	$151.64	$151.65	$151.60
Purchase #7	$139.53	7.209%	$149.5887	$149.59	$149.60	$149.60
7 purchase totals =	$785.90		$874.7306	$874.74	$874.80	$874.70