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	$104.33	6.719%	$111.3399	$111.34	$111.35	$111.30
Purchase #2	$35.34	10.690%	$39.1178	$39.12	$39.10	$39.10
Purchase #3	$224.27	4.411%	$234.1625	$234.16	$234.15	$234.20
Purchase #4	$162.36	3.709%	$168.3819	$168.38	$168.40	$168.40
Purchase #5	$222.71	12.121%	$249.7047	$249.70	$249.70	$249.70
Purchase #6	$105.27	7.668%	$113.3421	$113.34	$113.35	$113.30
Purchase #7	$57.40	10.230%	$63.272	$63.27	$63.25	$63.30
7 purchase totals =	$911.68		$979.3209	$979.31	$979.30	$979.30