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	$170.41	8.139%	$184.2797	$184.28	$184.30	$184.30
Purchase #2	$164.76	4.864%	$172.7739	$172.77	$172.75	$172.80
Purchase #3	$79.96	10.645%	$88.4717	$88.47	$88.45	$88.50
Purchase #4	$94.86	4.321%	$98.9589	$98.96	$98.95	$99.00
Purchase #5	$161.34	3.699%	$167.308	$167.31	$167.30	$167.30
Purchase #6	$119.91	6.184%	$127.3252	$127.33	$127.35	$127.30
Purchase #7	$218.28	11.442%	$243.2556	$243.26	$243.25	$243.30
7 purchase totals =	$1,009.52		$1,082.3730	$1,082.38	$1,082.35	$1,082.50