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	$243.61	11.602%	$271.8736	$271.87	$271.85	$271.90
Purchase #2	$54.29	6.257%	$57.6869	$57.69	$57.70	$57.70
Purchase #3	$100.50	10.639%	$111.1922	$111.19	$111.20	$111.20
Purchase #4	$149.94	12.811%	$169.1488	$169.15	$169.15	$169.10
Purchase #5	$116.40	10.162%	$128.2286	$128.23	$128.25	$128.20
Purchase #6	$97.36	9.811%	$106.912	$106.91	$106.90	$106.90
Purchase #7	$224.49	9.210%	$245.1655	$245.17	$245.15	$245.20
7 purchase totals =	$986.59		$1,090.2076	$1,090.21	$1,090.20	$1,090.20