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	$98.52	11.128%	$109.4833	$109.48	$109.50	$109.50
Purchase #2	$221.44	10.467%	$244.6181	$244.62	$244.60	$244.60
Purchase #3	$241.26	7.690%	$259.8129	$259.81	$259.80	$259.80
Purchase #4	$62.76	13.305%	$71.1102	$71.11	$71.10	$71.10
Purchase #5	$104.96	5.865%	$111.1159	$111.12	$111.10	$111.10
Purchase #6	$72.26	12.552%	$81.3301	$81.33	$81.35	$81.30
Purchase #7	$111.98	13.297%	$126.87	$126.87	$126.85	$126.90
7 purchase totals =	$913.18		$1,004.3405	$1,004.34	$1,004.30	$1,004.30