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	$227.83	9.871%	$250.3191	$250.32	$250.30	$250.30
Purchase #2	$104.88	12.750%	$118.2522	$118.25	$118.25	$118.30
Purchase #3	$117.35	7.250%	$125.8579	$125.86	$125.85	$125.90
Purchase #4	$241.77	13.259%	$273.8263	$273.83	$273.85	$273.80
Purchase #5	$125.62	13.765%	$142.9116	$142.91	$142.90	$142.90
Purchase #6	$246.83	7.490%	$265.3176	$265.32	$265.30	$265.30
Purchase #7	$10.51	10.520%	$11.6157	$11.62	$11.60	$11.60
7 purchase totals =	$1,074.79		$1,188.1004	$1,188.11	$1,188.05	$1,188.10