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	$171.30	5.615%	$180.9185	$180.92	$180.90	$180.90
Purchase #2	$211.28	6.668%	$225.3682	$225.37	$225.35	$225.40
Purchase #3	$79.87	7.108%	$85.5472	$85.55	$85.55	$85.50
Purchase #4	$240.77	12.117%	$269.9441	$269.94	$269.95	$269.90
Purchase #5	$69.45	5.857%	$73.5177	$73.52	$73.50	$73.50
Purchase #6	$203.56	3.591%	$210.8698	$210.87	$210.85	$210.90
Purchase #7	$37.86	12.172%	$42.4683	$42.47	$42.45	$42.50
7 purchase totals =	$1,014.09		$1,088.6338	$1,088.64	$1,088.55	$1,088.60