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	$33.97	12.433%	$38.1935	$38.19	$38.20	$38.20
Purchase #2	$61.94	9.634%	$67.9073	$67.91	$67.90	$67.90
Purchase #3	$189.59	4.847%	$198.7794	$198.78	$198.80	$198.80
Purchase #4	$196.60	12.598%	$221.3677	$221.37	$221.35	$221.40
Purchase #5	$47.60	12.218%	$53.4158	$53.42	$53.40	$53.40
Purchase #6	$123.31	10.570%	$136.3439	$136.34	$136.35	$136.30
Purchase #7	$165.72	8.688%	$180.1178	$180.12	$180.10	$180.10
7 purchase totals =	$818.73		$896.1254	$896.13	$896.10	$896.10