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	$132.33	9.212%	$144.5202	$144.52	$144.50	$144.50
Purchase #2	$246.25	13.348%	$279.1195	$279.12	$279.10	$279.10
Purchase #3	$188.28	5.576%	$198.7785	$198.78	$198.80	$198.80
Purchase #4	$236.61	6.316%	$251.5543	$251.55	$251.55	$251.60
Purchase #5	$77.34	6.381%	$82.2751	$82.28	$82.30	$82.30
Purchase #6	$99.95	9.274%	$109.2194	$109.22	$109.20	$109.20
Purchase #7	$223.34	5.700%	$236.0704	$236.07	$236.05	$236.10
7 purchase totals =	$1,204.10		$1,301.5374	$1,301.54	$1,301.50	$1,301.60