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	$143.64	5.776%	$151.9366	$151.94	$151.95	$151.90
Purchase #2	$46.31	8.710%	$50.3436	$50.34	$50.35	$50.30
Purchase #3	$165.32	13.701%	$187.9705	$187.97	$187.95	$188.00
Purchase #4	$72.25	6.355%	$76.8415	$76.84	$76.85	$76.80
Purchase #5	$238.51	12.564%	$268.4764	$268.48	$268.50	$268.50
Purchase #6	$172.62	7.220%	$185.0832	$185.08	$185.10	$185.10
Purchase #7	$227.93	13.814%	$259.4163	$259.42	$259.40	$259.40
7 purchase totals =	$1,066.58		$1,180.0681	$1,180.07	$1,180.10	$1,180.00