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	$101.92	9.480%	$111.582	$111.58	$111.60	$111.60
Purchase #2	$218.80	12.184%	$245.4586	$245.46	$245.45	$245.50
Purchase #3	$167.50	11.650%	$187.0138	$187.01	$187.00	$187.00
Purchase #4	$128.86	10.651%	$142.5849	$142.58	$142.60	$142.60
Purchase #5	$18.58	8.129%	$20.0904	$20.09	$20.10	$20.10
Purchase #6	$26.82	4.236%	$27.9561	$27.96	$27.95	$28.00
Purchase #7	$118.61	7.818%	$127.8829	$127.88	$127.90	$127.90
7 purchase totals =	$781.09		$862.5687	$862.56	$862.60	$862.70