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	$46.93	7.654%	$50.522	$50.52	$50.50	$50.50
Purchase #2	$43.83	8.191%	$47.4201	$47.42	$47.40	$47.40
Purchase #3	$194.80	4.564%	$203.6907	$203.69	$203.70	$203.70
Purchase #4	$36.36	3.765%	$37.729	$37.73	$37.75	$37.70
Purchase #5	$48.89	3.250%	$50.4789	$50.48	$50.50	$50.50
Purchase #6	$244.25	3.754%	$253.4191	$253.42	$253.40	$253.40
Purchase #7	$124.57	10.241%	$137.3272	$137.33	$137.35	$137.30
7 purchase totals =	$739.63		$780.5870	$780.59	$780.60	$780.50