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	$10.70	4.754%	$11.2087	$11.21	$11.20	$11.20
Purchase #2	$238.55	13.285%	$270.2414	$270.24	$270.25	$270.20
Purchase #3	$246.49	8.132%	$266.5346	$266.53	$266.55	$266.50
Purchase #4	$96.56	6.802%	$103.128	$103.13	$103.15	$103.10
Purchase #5	$33.47	13.329%	$37.9312	$37.93	$37.95	$37.90
Purchase #6	$243.69	6.184%	$258.7598	$258.76	$258.75	$258.80
Purchase #7	$26.25	9.816%	$28.8267	$28.83	$28.85	$28.80
7 purchase totals =	$895.71		$976.6304	$976.63	$976.70	$976.50