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	$248.91	11.788%	$278.2515	$278.25	$278.25	$278.30
Purchase #2	$127.30	9.283%	$139.1173	$139.12	$139.10	$139.10
Purchase #3	$202.66	9.548%	$222.01	$222.01	$222.00	$222.00
Purchase #4	$7.56	13.581%	$8.5867	$8.59	$8.60	$8.60
Purchase #5	$168.92	8.225%	$182.8137	$182.81	$182.80	$182.80
Purchase #6	$5.58	12.865%	$6.2979	$6.30	$6.30	$6.30
Purchase #7	$89.94	11.578%	$100.3533	$100.35	$100.35	$100.40
7 purchase totals =	$850.87		$937.4304	$937.43	$937.40	$937.50