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	$227.38	7.526%	$244.4926	$244.49	$244.50	$244.50
Purchase #2	$167.56	12.448%	$188.4179	$188.42	$188.40	$188.40
Purchase #3	$169.41	7.356%	$181.8718	$181.87	$181.85	$181.90
Purchase #4	$86.40	6.123%	$91.6903	$91.69	$91.70	$91.70
Purchase #5	$29.65	10.761%	$32.8406	$32.84	$32.85	$32.80
Purchase #6	$63.65	12.534%	$71.6279	$71.63	$71.65	$71.60
Purchase #7	$19.64	3.288%	$20.2858	$20.29	$20.30	$20.30
7 purchase totals =	$763.69		$831.2269	$831.23	$831.25	$831.20