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	$128.52	12.290%	$144.3151	$144.32	$144.30	$144.30
Purchase #2	$199.47	4.448%	$208.3424	$208.34	$208.35	$208.30
Purchase #3	$87.37	9.689%	$95.8353	$95.84	$95.85	$95.80
Purchase #4	$107.48	3.131%	$110.8452	$110.85	$110.85	$110.80
Purchase #5	$146.28	8.784%	$159.1292	$159.13	$159.15	$159.10
Purchase #6	$86.40	3.459%	$89.3886	$89.39	$89.40	$89.40
Purchase #7	$175.49	11.656%	$195.9451	$195.95	$195.95	$195.90
7 purchase totals =	$931.01		$1,003.8009	$1,003.82	$1,003.85	$1,003.60