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	$235.33	7.507%	$252.9962	$253.00	$253.00	$253.00
Purchase #2	$146.96	13.682%	$167.0671	$167.07	$167.05	$167.10
Purchase #3	$169.42	6.128%	$179.8021	$179.80	$179.80	$179.80
Purchase #4	$145.69	12.688%	$164.1751	$164.18	$164.20	$164.20
Purchase #5	$133.78	13.568%	$151.9313	$151.93	$151.95	$151.90
Purchase #6	$93.46	12.534%	$105.1743	$105.17	$105.15	$105.20
Purchase #7	$152.31	9.530%	$166.8251	$166.83	$166.85	$166.80
7 purchase totals =	$1,076.95		$1,187.9712	$1,187.98	$1,188.00	$1,188.00