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	$150.56	3.513%	$155.8492	$155.85	$155.85	$155.80
Purchase #2	$140.40	6.507%	$149.5358	$149.54	$149.55	$149.50
Purchase #3	$37.61	3.793%	$39.0365	$39.04	$39.05	$39.00
Purchase #4	$198.85	13.709%	$226.1103	$226.11	$226.10	$226.10
Purchase #5	$57.58	3.727%	$59.726	$59.73	$59.75	$59.70
Purchase #6	$209.59	4.565%	$219.1578	$219.16	$219.15	$219.20
Purchase #7	$142.51	9.177%	$155.5881	$155.59	$155.60	$155.60
7 purchase totals =	$937.10		$1,005.0037	$1,005.02	$1,005.05	$1,004.90