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	$88.38	13.215%	$100.0594	$100.06	$100.05	$100.10
Purchase #2	$193.74	5.199%	$203.8125	$203.81	$203.80	$203.80
Purchase #3	$187.94	4.561%	$196.5119	$196.51	$196.50	$196.50
Purchase #4	$51.65	4.399%	$53.9221	$53.92	$53.90	$53.90
Purchase #5	$90.73	12.610%	$102.1711	$102.17	$102.15	$102.20
Purchase #6	$123.86	11.658%	$138.2996	$138.30	$138.30	$138.30
Purchase #7	$207.38	6.620%	$221.1086	$221.11	$221.10	$221.10
7 purchase totals =	$943.68		$1,015.8852	$1,015.88	$1,015.80	$1,015.90