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	$180.80	3.611%	$187.3287	$187.33	$187.35	$187.30
Purchase #2	$99.70	10.151%	$109.8205	$109.82	$109.80	$109.80
Purchase #3	$224.50	12.595%	$252.7758	$252.78	$252.80	$252.80
Purchase #4	$79.49	4.754%	$83.269	$83.27	$83.25	$83.30
Purchase #5	$126.98	6.143%	$134.7804	$134.78	$134.80	$134.80
Purchase #6	$78.30	9.585%	$85.8051	$85.81	$85.80	$85.80
Purchase #7	$214.77	10.510%	$237.3423	$237.34	$237.35	$237.30
7 purchase totals =	$1,004.54		$1,091.1218	$1,091.13	$1,091.15	$1,091.10