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	$250.37	13.440%	$284.0197	$284.02	$284.00	$284.00
Purchase #2	$39.71	4.745%	$41.5942	$41.59	$41.60	$41.60
Purchase #3	$233.50	11.242%	$259.7501	$259.75	$259.75	$259.80
Purchase #4	$41.34	11.205%	$45.9721	$45.97	$45.95	$46.00
Purchase #5	$89.69	6.489%	$95.51	$95.51	$95.50	$95.50
Purchase #6	$204.51	7.147%	$219.1263	$219.13	$219.15	$219.10
Purchase #7	$83.87	12.474%	$94.3319	$94.33	$94.35	$94.30
7 purchase totals =	$942.99		$1,040.3043	$1,040.30	$1,040.30	$1,040.30