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	$156.43	8.747%	$170.1129	$170.11	$170.10	$170.10
Purchase #2	$249.36	5.800%	$263.8229	$263.82	$263.80	$263.80
Purchase #3	$79.75	12.165%	$89.4516	$89.45	$89.45	$89.50
Purchase #4	$97.53	4.700%	$102.1139	$102.11	$102.10	$102.10
Purchase #5	$33.43	5.371%	$35.2255	$35.23	$35.25	$35.20
Purchase #6	$196.82	9.773%	$216.0552	$216.06	$216.05	$216.10
Purchase #7	$206.43	7.677%	$222.2776	$222.28	$222.30	$222.30
7 purchase totals =	$1,019.75		$1,099.0596	$1,099.06	$1,099.05	$1,099.10