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	$145.47	9.394%	$159.1355	$159.14	$159.15	$159.10
Purchase #2	$93.73	6.597%	$99.9134	$99.91	$99.90	$99.90
Purchase #3	$223.75	3.852%	$232.3689	$232.37	$232.35	$232.40
Purchase #4	$105.39	8.770%	$114.6327	$114.63	$114.65	$114.60
Purchase #5	$249.67	3.790%	$259.1325	$259.13	$259.15	$259.10
Purchase #6	$69.93	12.373%	$78.5824	$78.58	$78.60	$78.60
Purchase #7	$63.45	12.607%	$71.4491	$71.45	$71.45	$71.40
7 purchase totals =	$951.39		$1,015.2145	$1,015.21	$1,015.25	$1,015.10