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	$88.80	12.437%	$99.8441	$99.84	$99.85	$99.80
Purchase #2	$43.82	8.444%	$47.5202	$47.52	$47.50	$47.50
Purchase #3	$121.81	11.569%	$135.9022	$135.90	$135.90	$135.90
Purchase #4	$142.76	9.830%	$156.7933	$156.79	$156.80	$156.80
Purchase #5	$172.41	7.569%	$185.4597	$185.46	$185.45	$185.50
Purchase #6	$51.25	7.695%	$55.1937	$55.19	$55.20	$55.20
Purchase #7	$114.71	10.467%	$126.7167	$126.72	$126.70	$126.70
7 purchase totals =	$735.56		$807.4299	$807.42	$807.40	$807.40