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	$78.80	13.301%	$89.2812	$89.28	$89.30	$89.30
Purchase #2	$143.53	4.235%	$149.6085	$149.61	$149.60	$149.60
Purchase #3	$210.63	13.164%	$238.3573	$238.36	$238.35	$238.40
Purchase #4	$136.46	6.198%	$144.9178	$144.92	$144.90	$144.90
Purchase #5	$250.60	13.307%	$283.9473	$283.95	$283.95	$283.90
Purchase #6	$98.78	7.539%	$106.227	$106.23	$106.25	$106.20
Purchase #7	$24.74	11.847%	$27.6709	$27.67	$27.65	$27.70
7 purchase totals =	$943.54		$1,040.0100	$1,040.02	$1,040.00	$1,040.00