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	$20.89	10.365%	$23.0552	$23.06	$23.05	$23.10
Purchase #2	$36.28	10.765%	$40.1855	$40.19	$40.20	$40.20
Purchase #3	$16.48	12.384%	$18.5209	$18.52	$18.50	$18.50
Purchase #4	$117.65	11.407%	$131.0703	$131.07	$131.05	$131.10
Purchase #5	$24.87	9.479%	$27.2274	$27.23	$27.25	$27.20
Purchase #6	$141.85	12.688%	$159.8479	$159.85	$159.85	$159.80
Purchase #7	$35.39	4.272%	$36.9019	$36.90	$36.90	$36.90
7 purchase totals =	$393.41		$436.8091	$436.82	$436.80	$436.80