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	$29.51	10.240%	$32.5318	$32.53	$32.55	$32.50
Purchase #2	$160.39	6.245%	$170.4064	$170.41	$170.40	$170.40
Purchase #3	$185.54	5.727%	$196.1659	$196.17	$196.15	$196.20
Purchase #4	$224.49	7.479%	$241.2796	$241.28	$241.30	$241.30
Purchase #5	$161.47	6.419%	$171.8348	$171.83	$171.85	$171.80
Purchase #6	$37.99	7.794%	$40.9509	$40.95	$40.95	$41.00
Purchase #7	$162.57	3.676%	$168.5461	$168.55	$168.55	$168.50
7 purchase totals =	$961.96		$1,021.7155	$1,021.72	$1,021.75	$1,021.70