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	$250.56	13.786%	$285.1022	$285.10	$285.10	$285.10
Purchase #2	$65.98	5.325%	$69.4934	$69.49	$69.50	$69.50
Purchase #3	$64.96	3.668%	$67.3427	$67.34	$67.35	$67.30
Purchase #4	$131.84	10.268%	$145.3773	$145.38	$145.40	$145.40
Purchase #5	$199.68	6.793%	$213.2443	$213.24	$213.25	$213.20
Purchase #6	$132.25	6.280%	$140.5553	$140.56	$140.55	$140.60
Purchase #7	$156.93	5.378%	$165.3697	$165.37	$165.35	$165.40
7 purchase totals =	$1,002.20		$1,086.4849	$1,086.48	$1,086.50	$1,086.50