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	$209.94	13.481%	$238.242	$238.24	$238.25	$238.20
Purchase #2	$35.92	10.802%	$39.8001	$39.80	$39.80	$39.80
Purchase #3	$83.72	9.699%	$91.84	$91.84	$91.85	$91.80
Purchase #4	$120.31	13.564%	$136.6288	$136.63	$136.65	$136.60
Purchase #5	$165.48	12.820%	$186.6945	$186.69	$186.70	$186.70
Purchase #6	$181.33	3.701%	$188.041	$188.04	$188.05	$188.00
Purchase #7	$95.48	5.487%	$100.719	$100.72	$100.70	$100.70
7 purchase totals =	$892.18		$981.9654	$981.96	$982.00	$981.80