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	$11.61	10.245%	$12.7994	$12.80	$12.80	$12.80
Purchase #2	$157.51	10.583%	$174.1793	$174.18	$174.20	$174.20
Purchase #3	$188.36	4.316%	$196.4896	$196.49	$196.50	$196.50
Purchase #4	$64.90	4.377%	$67.7407	$67.74	$67.75	$67.70
Purchase #5	$173.47	10.525%	$191.7277	$191.73	$191.75	$191.70
Purchase #6	$173.64	12.765%	$195.8051	$195.81	$195.80	$195.80
Purchase #7	$218.69	11.841%	$244.5851	$244.59	$244.60	$244.60
7 purchase totals =	$988.18		$1,083.3269	$1,083.34	$1,083.40	$1,083.30