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	$37.79	12.825%	$42.6366	$42.64	$42.65	$42.60
Purchase #2	$140.36	13.215%	$158.9086	$158.91	$158.90	$158.90
Purchase #3	$9.45	11.121%	$10.5009	$10.50	$10.50	$10.50
Purchase #4	$159.74	4.534%	$166.9826	$166.98	$167.00	$167.00
Purchase #5	$243.81	10.779%	$270.0903	$270.09	$270.10	$270.10
Purchase #6	$215.99	3.418%	$223.3725	$223.37	$223.35	$223.40
Purchase #7	$201.89	5.666%	$213.3291	$213.33	$213.35	$213.30
7 purchase totals =	$1,009.03		$1,085.8206	$1,085.82	$1,085.85	$1,085.80