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	$58.84	12.692%	$66.308	$66.31	$66.30	$66.30
Purchase #2	$139.79	11.421%	$155.7554	$155.76	$155.75	$155.80
Purchase #3	$151.64	10.169%	$167.0603	$167.06	$167.05	$167.10
Purchase #4	$243.56	12.271%	$273.4472	$273.45	$273.45	$273.40
Purchase #5	$249.75	7.415%	$268.269	$268.27	$268.25	$268.30
Purchase #6	$89.69	11.147%	$99.6877	$99.69	$99.70	$99.70
Purchase #7	$75.54	3.841%	$78.4415	$78.44	$78.45	$78.40
7 purchase totals =	$1,008.81		$1,108.9691	$1,108.98	$1,108.95	$1,109.00