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	$40.50	11.360%	$45.1008	$45.10	$45.10	$45.10
Purchase #2	$40.91	11.585%	$45.6494	$45.65	$45.65	$45.60
Purchase #3	$195.89	4.270%	$204.2545	$204.25	$204.25	$204.30
Purchase #4	$95.57	9.341%	$104.4972	$104.50	$104.50	$104.50
Purchase #5	$143.83	11.404%	$160.2324	$160.23	$160.25	$160.20
Purchase #6	$162.59	4.569%	$170.0187	$170.02	$170.00	$170.00
Purchase #7	$63.56	10.102%	$69.9808	$69.98	$70.00	$70.00
7 purchase totals =	$742.85		$799.7338	$799.73	$799.75	$799.70