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	$228.33	9.382%	$249.7519	$249.75	$249.75	$249.80
Purchase #2	$83.49	12.871%	$94.236	$94.24	$94.25	$94.20
Purchase #3	$58.54	11.568%	$65.3119	$65.31	$65.30	$65.30
Purchase #4	$116.92	12.158%	$131.1351	$131.14	$131.15	$131.10
Purchase #5	$51.97	5.584%	$54.872	$54.87	$54.85	$54.90
Purchase #6	$37.53	8.450%	$40.7013	$40.70	$40.70	$40.70
Purchase #7	$248.86	5.220%	$261.8505	$261.85	$261.85	$261.90
7 purchase totals =	$825.64		$897.8587	$897.86	$897.85	$897.90