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	$142.55	11.585%	$159.0644	$159.06	$159.05	$159.10
Purchase #2	$156.41	10.281%	$172.4905	$172.49	$172.50	$172.50
Purchase #3	$125.35	12.563%	$141.0977	$141.10	$141.10	$141.10
Purchase #4	$143.71	4.465%	$150.1267	$150.13	$150.15	$150.10
Purchase #5	$136.74	3.788%	$141.9197	$141.92	$141.90	$141.90
Purchase #6	$84.31	6.507%	$89.7961	$89.80	$89.80	$89.80
Purchase #7	$136.79	7.552%	$147.1204	$147.12	$147.10	$147.10
7 purchase totals =	$925.86		$1,001.6155	$1,001.62	$1,001.60	$1,001.60