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	$74.85	4.363%	$78.1157	$78.12	$78.10	$78.10
Purchase #2	$74.32	8.407%	$80.5681	$80.57	$80.55	$80.60
Purchase #3	$160.42	4.195%	$167.1496	$167.15	$167.15	$167.10
Purchase #4	$206.79	12.721%	$233.0958	$233.10	$233.10	$233.10
Purchase #5	$238.56	10.335%	$263.2152	$263.22	$263.20	$263.20
Purchase #6	$28.86	13.750%	$32.8283	$32.83	$32.85	$32.80
Purchase #7	$91.55	7.494%	$98.4108	$98.41	$98.40	$98.40
7 purchase totals =	$875.35		$953.3835	$953.40	$953.35	$953.30