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	$153.84	13.414%	$174.4761	$174.48	$174.50	$174.50
Purchase #2	$50.45	10.697%	$55.8466	$55.85	$55.85	$55.80
Purchase #3	$44.85	6.850%	$47.9222	$47.92	$47.90	$47.90
Purchase #4	$7.29	8.404%	$7.9027	$7.90	$7.90	$7.90
Purchase #5	$173.49	12.656%	$195.4469	$195.45	$195.45	$195.40
Purchase #6	$74.81	5.334%	$78.8004	$78.80	$78.80	$78.80
Purchase #7	$105.28	5.363%	$110.9262	$110.93	$110.95	$110.90
7 purchase totals =	$610.01		$671.3211	$671.33	$671.35	$671.20