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	$28.63	13.816%	$32.5855	$32.59	$32.60	$32.60
Purchase #2	$234.52	6.230%	$249.1306	$249.13	$249.15	$249.10
Purchase #3	$96.53	7.631%	$103.8962	$103.90	$103.90	$103.90
Purchase #4	$240.71	9.799%	$264.2972	$264.30	$264.30	$264.30
Purchase #5	$104.87	6.327%	$111.5051	$111.51	$111.50	$111.50
Purchase #6	$168.92	13.706%	$192.0722	$192.07	$192.05	$192.10
Purchase #7	$174.29	8.673%	$189.4062	$189.41	$189.40	$189.40
7 purchase totals =	$1,048.47		$1,142.8930	$1,142.91	$1,142.90	$1,142.90