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	$129.95	12.540%	$146.2457	$146.25	$146.25	$146.20
Purchase #2	$172.76	7.341%	$185.4423	$185.44	$185.45	$185.40
Purchase #3	$99.89	3.108%	$102.9946	$102.99	$103.00	$103.00
Purchase #4	$155.67	4.432%	$162.5693	$162.57	$162.55	$162.60
Purchase #5	$175.50	13.260%	$198.7713	$198.77	$198.75	$198.80
Purchase #6	$203.41	3.615%	$210.7633	$210.76	$210.75	$210.80
Purchase #7	$76.39	9.621%	$83.7395	$83.74	$83.75	$83.70
7 purchase totals =	$1,013.57		$1,090.5260	$1,090.52	$1,090.50	$1,090.50