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	$148.84	6.842%	$159.0236	$159.02	$159.00	$159.00
Purchase #2	$226.78	6.170%	$240.7723	$240.77	$240.75	$240.80
Purchase #3	$98.34	13.226%	$111.3464	$111.35	$111.35	$111.30
Purchase #4	$118.43	4.509%	$123.77	$123.77	$123.75	$123.80
Purchase #5	$85.29	11.535%	$95.1282	$95.13	$95.15	$95.10
Purchase #6	$70.56	11.826%	$78.9044	$78.90	$78.90	$78.90
Purchase #7	$245.62	9.601%	$269.202	$269.20	$269.20	$269.20
7 purchase totals =	$993.86		$1,078.1469	$1,078.14	$1,078.10	$1,078.10