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	$83.46	6.784%	$89.1219	$89.12	$89.10	$89.10
Purchase #2	$148.44	10.624%	$164.2103	$164.21	$164.20	$164.20
Purchase #3	$35.54	4.224%	$37.0412	$37.04	$37.05	$37.00
Purchase #4	$104.67	9.640%	$114.7602	$114.76	$114.75	$114.80
Purchase #5	$239.61	3.650%	$248.3558	$248.36	$248.35	$248.40
Purchase #6	$198.46	3.604%	$205.6125	$205.61	$205.60	$205.60
Purchase #7	$244.60	6.712%	$261.0176	$261.02	$261.00	$261.00
7 purchase totals =	$1,054.78		$1,120.1195	$1,120.12	$1,120.05	$1,120.10