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	$56.58	13.697%	$64.3298	$64.33	$64.35	$64.30
Purchase #2	$29.31	10.299%	$32.3286	$32.33	$32.35	$32.30
Purchase #3	$200.56	4.657%	$209.9001	$209.90	$209.90	$209.90
Purchase #4	$227.66	10.195%	$250.8699	$250.87	$250.85	$250.90
Purchase #5	$210.75	6.230%	$223.8797	$223.88	$223.90	$223.90
Purchase #6	$14.62	4.717%	$15.3096	$15.31	$15.30	$15.30
Purchase #7	$208.67	12.215%	$234.159	$234.16	$234.15	$234.20
7 purchase totals =	$948.15		$1,030.7767	$1,030.78	$1,030.80	$1,030.80