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	$70.39	9.223%	$76.8821	$76.88	$76.90	$76.90
Purchase #2	$221.63	3.426%	$229.223	$229.22	$229.20	$229.20
Purchase #3	$183.49	3.739%	$190.3507	$190.35	$190.35	$190.40
Purchase #4	$184.76	7.371%	$198.3787	$198.38	$198.40	$198.40
Purchase #5	$204.85	9.279%	$223.858	$223.86	$223.85	$223.90
Purchase #6	$214.62	8.608%	$233.0945	$233.09	$233.10	$233.10
Purchase #7	$87.48	3.269%	$90.3397	$90.34	$90.35	$90.30
7 purchase totals =	$1,167.22		$1,242.1267	$1,242.12	$1,242.15	$1,242.20