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	$28.91	11.264%	$32.1664	$32.17	$32.15	$32.20
Purchase #2	$169.75	13.401%	$192.4982	$192.50	$192.50	$192.50
Purchase #3	$117.98	8.404%	$127.895	$127.90	$127.90	$127.90
Purchase #4	$221.37	12.544%	$249.1387	$249.14	$249.15	$249.10
Purchase #5	$219.88	5.696%	$232.4044	$232.40	$232.40	$232.40
Purchase #6	$88.65	3.256%	$91.5364	$91.54	$91.55	$91.50
Purchase #7	$11.93	13.127%	$13.4961	$13.50	$13.50	$13.50
7 purchase totals =	$858.47		$939.1352	$939.15	$939.15	$939.10