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	$226.98	11.800%	$253.7636	$253.76	$253.75	$253.80
Purchase #2	$245.64	6.313%	$261.1473	$261.15	$261.15	$261.10
Purchase #3	$69.95	13.206%	$79.1876	$79.19	$79.20	$79.20
Purchase #4	$32.38	4.569%	$33.8594	$33.86	$33.85	$33.90
Purchase #5	$93.50	13.212%	$105.8532	$105.85	$105.85	$105.90
Purchase #6	$134.25	9.108%	$146.4775	$146.48	$146.50	$146.50
Purchase #7	$221.46	13.570%	$251.5121	$251.51	$251.50	$251.50
7 purchase totals =	$1,024.16		$1,131.8007	$1,131.80	$1,131.80	$1,131.90