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	$166.64	10.780%	$184.6038	$184.60	$184.60	$184.60
Purchase #2	$196.25	11.284%	$218.3949	$218.39	$218.40	$218.40
Purchase #3	$125.69	13.148%	$142.2157	$142.22	$142.20	$142.20
Purchase #4	$165.57	4.265%	$172.6316	$172.63	$172.65	$172.60
Purchase #5	$219.65	10.372%	$242.4321	$242.43	$242.45	$242.40
Purchase #6	$243.67	8.317%	$263.936	$263.94	$263.95	$263.90
Purchase #7	$156.30	10.219%	$172.2723	$172.27	$172.25	$172.30
7 purchase totals =	$1,273.77		$1,396.4864	$1,396.48	$1,396.50	$1,396.40