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	$145.84	9.750%	$160.0594	$160.06	$160.05	$160.10
Purchase #2	$110.79	11.646%	$123.6926	$123.69	$123.70	$123.70
Purchase #3	$84.53	8.791%	$91.961	$91.96	$91.95	$92.00
Purchase #4	$89.37	10.799%	$99.0211	$99.02	$99.00	$99.00
Purchase #5	$239.96	10.340%	$264.7719	$264.77	$264.75	$264.80
Purchase #6	$68.51	4.545%	$71.6238	$71.62	$71.60	$71.60
Purchase #7	$239.94	12.120%	$269.0207	$269.02	$269.00	$269.00
7 purchase totals =	$978.94		$1,080.1505	$1,080.14	$1,080.05	$1,080.20