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	$250.44	11.195%	$278.4768	$278.48	$278.50	$278.50
Purchase #2	$214.74	3.856%	$223.0204	$223.02	$223.00	$223.00
Purchase #3	$80.81	11.253%	$89.9035	$89.90	$89.90	$89.90
Purchase #4	$5.73	10.745%	$6.3457	$6.35	$6.35	$6.30
Purchase #5	$146.94	12.216%	$164.8902	$164.89	$164.90	$164.90
Purchase #6	$30.35	8.749%	$33.0053	$33.01	$33.00	$33.00
Purchase #7	$232.69	4.650%	$243.5101	$243.51	$243.50	$243.50
7 purchase totals =	$961.70		$1,039.1520	$1,039.16	$1,039.15	$1,039.10