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	$145.94	6.286%	$155.1138	$155.11	$155.10	$155.10
Purchase #2	$26.28	12.759%	$29.6331	$29.63	$29.65	$29.60
Purchase #3	$237.87	12.384%	$267.3278	$267.33	$267.35	$267.30
Purchase #4	$127.67	11.626%	$142.5129	$142.51	$142.50	$142.50
Purchase #5	$28.29	12.135%	$31.723	$31.72	$31.70	$31.70
Purchase #6	$170.48	8.231%	$184.5122	$184.51	$184.50	$184.50
Purchase #7	$196.79	13.585%	$223.5239	$223.52	$223.50	$223.50
7 purchase totals =	$933.32		$1,034.3467	$1,034.33	$1,034.30	$1,034.20