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	$27.51	8.196%	$29.7647	$29.76	$29.75	$29.80
Purchase #2	$198.43	7.283%	$212.8817	$212.88	$212.90	$212.90
Purchase #3	$197.35	7.427%	$212.0072	$212.01	$212.00	$212.00
Purchase #4	$250.93	11.410%	$279.5611	$279.56	$279.55	$279.60
Purchase #5	$6.52	11.554%	$7.2733	$7.27	$7.25	$7.30
Purchase #6	$87.74	7.557%	$94.3705	$94.37	$94.35	$94.40
Purchase #7	$137.46	3.581%	$142.3824	$142.38	$142.40	$142.40
7 purchase totals =	$905.94		$978.2409	$978.23	$978.20	$978.40