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	$183.42	3.247%	$189.3756	$189.38	$189.40	$189.40
Purchase #2	$153.35	3.796%	$159.1712	$159.17	$159.15	$159.20
Purchase #3	$86.25	4.708%	$90.3107	$90.31	$90.30	$90.30
Purchase #4	$215.82	7.362%	$231.7087	$231.71	$231.70	$231.70
Purchase #5	$148.87	11.459%	$165.929	$165.93	$165.95	$165.90
Purchase #6	$63.86	11.559%	$71.2416	$71.24	$71.25	$71.20
Purchase #7	$82.58	9.266%	$90.2319	$90.23	$90.25	$90.20
7 purchase totals =	$934.15		$997.9687	$997.97	$998.00	$997.90