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	$130.71	5.155%	$137.4481	$137.45	$137.45	$137.40
Purchase #2	$111.92	5.364%	$117.9234	$117.92	$117.90	$117.90
Purchase #3	$30.34	10.622%	$33.5627	$33.56	$33.55	$33.60
Purchase #4	$98.38	11.557%	$109.7498	$109.75	$109.75	$109.70
Purchase #5	$86.97	9.841%	$95.5287	$95.53	$95.55	$95.50
Purchase #6	$41.33	13.530%	$46.9219	$46.92	$46.90	$46.90
Purchase #7	$48.91	10.696%	$54.1414	$54.14	$54.15	$54.10
7 purchase totals =	$548.56		$595.2760	$595.27	$595.25	$595.10