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	$92.46	10.661%	$102.3172	$102.32	$102.30	$102.30
Purchase #2	$205.35	11.750%	$229.4786	$229.48	$229.50	$229.50
Purchase #3	$50.94	11.685%	$56.8923	$56.89	$56.90	$56.90
Purchase #4	$145.62	4.392%	$152.0156	$152.02	$152.00	$152.00
Purchase #5	$43.75	6.268%	$46.4923	$46.49	$46.50	$46.50
Purchase #6	$122.82	4.325%	$128.132	$128.13	$128.15	$128.10
Purchase #7	$84.55	12.606%	$95.2084	$95.21	$95.20	$95.20
7 purchase totals =	$745.49		$810.5364	$810.54	$810.55	$810.50