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	$73.43	7.269%	$78.7676	$78.77	$78.75	$78.80
Purchase #2	$211.93	12.630%	$238.6968	$238.70	$238.70	$238.70
Purchase #3	$205.87	7.748%	$221.8208	$221.82	$221.80	$221.80
Purchase #4	$33.98	8.745%	$36.9516	$36.95	$36.95	$37.00
Purchase #5	$103.93	8.594%	$112.8617	$112.86	$112.85	$112.90
Purchase #6	$219.90	13.570%	$249.7404	$249.74	$249.75	$249.70
Purchase #7	$89.29	12.164%	$100.1512	$100.15	$100.15	$100.20
7 purchase totals =	$938.33		$1,038.9901	$1,038.99	$1,038.95	$1,039.10