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	$133.35	6.821%	$142.4458	$142.45	$142.45	$142.40
Purchase #2	$140.84	8.122%	$152.279	$152.28	$152.30	$152.30
Purchase #3	$116.26	12.871%	$131.2238	$131.22	$131.20	$131.20
Purchase #4	$63.46	11.159%	$70.5415	$70.54	$70.55	$70.50
Purchase #5	$128.82	7.123%	$137.9958	$138.00	$138.00	$138.00
Purchase #6	$46.63	12.173%	$52.3063	$52.31	$52.30	$52.30
Purchase #7	$43.55	3.593%	$45.1148	$45.11	$45.10	$45.10
7 purchase totals =	$672.91		$731.9070	$731.91	$731.90	$731.80