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	$28.45	10.693%	$31.4922	$31.49	$31.50	$31.50
Purchase #2	$189.83	11.110%	$210.9201	$210.92	$210.90	$210.90
Purchase #3	$112.49	11.238%	$125.1316	$125.13	$125.15	$125.10
Purchase #4	$95.37	3.309%	$98.5258	$98.53	$98.55	$98.50
Purchase #5	$105.52	6.673%	$112.5613	$112.56	$112.55	$112.60
Purchase #6	$46.72	13.869%	$53.1996	$53.20	$53.20	$53.20
Purchase #7	$64.44	5.203%	$67.7928	$67.79	$67.80	$67.80
7 purchase totals =	$642.82		$699.6234	$699.62	$699.65	$699.60