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	$115.53	3.251%	$119.2859	$119.29	$119.30	$119.30
Purchase #2	$244.47	3.126%	$252.1121	$252.11	$252.10	$252.10
Purchase #3	$84.98	6.651%	$90.632	$90.63	$90.65	$90.60
Purchase #4	$240.88	9.291%	$263.2602	$263.26	$263.25	$263.30
Purchase #5	$154.34	10.702%	$170.8575	$170.86	$170.85	$170.90
Purchase #6	$31.69	5.707%	$33.4985	$33.50	$33.50	$33.50
Purchase #7	$105.44	3.676%	$109.316	$109.32	$109.30	$109.30
7 purchase totals =	$977.33		$1,038.9622	$1,038.97	$1,038.95	$1,039.00