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	$115.44	12.228%	$129.556	$129.56	$129.55	$129.60
Purchase #2	$113.57	5.826%	$120.1866	$120.19	$120.20	$120.20
Purchase #3	$31.72	11.586%	$35.3951	$35.40	$35.40	$35.40
Purchase #4	$173.36	13.537%	$196.8277	$196.83	$196.85	$196.80
Purchase #5	$147.93	12.555%	$166.5026	$166.50	$166.50	$166.50
Purchase #6	$82.34	9.203%	$89.9178	$89.92	$89.90	$89.90
Purchase #7	$160.54	7.182%	$172.07	$172.07	$172.05	$172.10
7 purchase totals =	$824.90		$910.4558	$910.47	$910.45	$910.50