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	$12.90	10.621%	$14.2701	$14.27	$14.25	$14.30
Purchase #2	$171.81	9.315%	$187.8141	$187.81	$187.80	$187.80
Purchase #3	$17.73	5.596%	$18.7222	$18.72	$18.70	$18.70
Purchase #4	$167.98	13.325%	$190.3633	$190.36	$190.35	$190.40
Purchase #5	$98.35	5.378%	$103.6393	$103.64	$103.65	$103.60
Purchase #6	$241.89	6.205%	$256.8993	$256.90	$256.90	$256.90
Purchase #7	$165.35	10.480%	$182.6787	$182.68	$182.70	$182.70
7 purchase totals =	$876.01		$954.3870	$954.38	$954.35	$954.40