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	$56.77	3.725%	$58.8847	$58.88	$58.90	$58.90
Purchase #2	$69.38	3.191%	$71.5939	$71.59	$71.60	$71.60
Purchase #3	$49.59	9.660%	$54.3804	$54.38	$54.40	$54.40
Purchase #4	$81.41	4.820%	$85.334	$85.33	$85.35	$85.30
Purchase #5	$146.53	4.229%	$152.7268	$152.73	$152.75	$152.70
Purchase #6	$131.44	8.227%	$142.2536	$142.25	$142.25	$142.30
Purchase #7	$237.38	12.743%	$267.6293	$267.63	$267.65	$267.60
7 purchase totals =	$772.50		$832.8027	$832.79	$832.90	$832.80