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	$121.66	4.681%	$127.3549	$127.35	$127.35	$127.40
Purchase #2	$144.98	7.711%	$156.1594	$156.16	$156.15	$156.20
Purchase #3	$84.92	6.306%	$90.2751	$90.28	$90.30	$90.30
Purchase #4	$13.42	10.471%	$14.8252	$14.83	$14.85	$14.80
Purchase #5	$114.38	11.356%	$127.369	$127.37	$127.35	$127.40
Purchase #6	$120.82	8.432%	$131.0075	$131.01	$131.00	$131.00
Purchase #7	$219.93	9.200%	$240.1636	$240.16	$240.15	$240.20
7 purchase totals =	$820.11		$887.1547	$887.16	$887.15	$887.30