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	$111.39	5.490%	$117.5053	$117.51	$117.50	$117.50
Purchase #2	$6.31	5.272%	$6.6427	$6.64	$6.65	$6.60
Purchase #3	$80.57	12.695%	$90.7984	$90.80	$90.80	$90.80
Purchase #4	$196.82	13.673%	$223.7312	$223.73	$223.75	$223.70
Purchase #5	$12.64	5.262%	$13.3051	$13.31	$13.30	$13.30
Purchase #6	$192.66	12.132%	$216.0335	$216.03	$216.05	$216.00
Purchase #7	$105.86	10.695%	$117.1817	$117.18	$117.20	$117.20
7 purchase totals =	$706.25		$785.1979	$785.20	$785.25	$785.10