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	$242.64	12.800%	$273.6979	$273.70	$273.70	$273.70
Purchase #2	$173.27	10.133%	$190.8274	$190.83	$190.85	$190.80
Purchase #3	$243.69	10.154%	$268.4343	$268.43	$268.45	$268.40
Purchase #4	$59.27	7.264%	$63.5754	$63.58	$63.60	$63.60
Purchase #5	$238.82	13.656%	$271.4333	$271.43	$271.45	$271.40
Purchase #6	$92.91	3.833%	$96.4712	$96.47	$96.45	$96.50
Purchase #7	$54.27	9.190%	$59.2574	$59.26	$59.25	$59.30
7 purchase totals =	$1,104.87		$1,223.6969	$1,223.70	$1,223.75	$1,223.70