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	$49.96	13.599%	$56.7541	$56.75	$56.75	$56.80
Purchase #2	$54.54	7.430%	$58.5923	$58.59	$58.60	$58.60
Purchase #3	$148.25	11.710%	$165.6101	$165.61	$165.60	$165.60
Purchase #4	$150.32	11.700%	$167.9074	$167.91	$167.90	$167.90
Purchase #5	$101.86	8.156%	$110.1677	$110.17	$110.15	$110.20
Purchase #6	$118.38	7.570%	$127.3414	$127.34	$127.35	$127.30
Purchase #7	$112.74	10.413%	$124.4796	$124.48	$124.50	$124.50
7 purchase totals =	$736.05		$810.8526	$810.85	$810.85	$810.90