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	$108.60	10.519%	$120.0236	$120.02	$120.00	$120.00
Purchase #2	$42.94	6.439%	$45.7049	$45.70	$45.70	$45.70
Purchase #3	$94.46	5.808%	$99.9462	$99.95	$99.95	$99.90
Purchase #4	$117.46	13.427%	$133.2314	$133.23	$133.25	$133.20
Purchase #5	$239.67	6.763%	$255.8789	$255.88	$255.90	$255.90
Purchase #6	$235.69	10.166%	$259.6502	$259.65	$259.65	$259.70
Purchase #7	$50.31	3.570%	$52.1061	$52.11	$52.10	$52.10
7 purchase totals =	$889.13		$966.5413	$966.54	$966.55	$966.50