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	$71.29	10.809%	$78.9957	$79.00	$79.00	$79.00
Purchase #2	$224.76	11.211%	$249.9578	$249.96	$249.95	$250.00
Purchase #3	$118.31	3.618%	$122.5905	$122.59	$122.60	$122.60
Purchase #4	$57.26	3.215%	$59.1009	$59.10	$59.10	$59.10
Purchase #5	$40.36	13.217%	$45.6944	$45.69	$45.70	$45.70
Purchase #6	$177.66	10.711%	$196.6892	$196.69	$196.70	$196.70
Purchase #7	$111.62	13.642%	$126.8472	$126.85	$126.85	$126.80
7 purchase totals =	$801.26		$879.8757	$879.88	$879.90	$879.90