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	$86.84	3.627%	$89.9897	$89.99	$90.00	$90.00
Purchase #2	$88.89	11.134%	$98.787	$98.79	$98.80	$98.80
Purchase #3	$153.64	9.319%	$167.9577	$167.96	$167.95	$168.00
Purchase #4	$27.86	5.105%	$29.2823	$29.28	$29.30	$29.30
Purchase #5	$85.71	4.290%	$89.387	$89.39	$89.40	$89.40
Purchase #6	$159.65	10.834%	$176.9465	$176.95	$176.95	$176.90
Purchase #7	$36.37	8.356%	$39.4091	$39.41	$39.40	$39.40
7 purchase totals =	$638.96		$691.7593	$691.77	$691.80	$691.80