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	$242.88	12.467%	$273.1598	$273.16	$273.15	$273.20
Purchase #2	$196.99	8.136%	$213.0171	$213.02	$213.00	$213.00
Purchase #3	$229.86	6.162%	$244.024	$244.02	$244.00	$244.00
Purchase #4	$137.40	3.346%	$141.9974	$142.00	$142.00	$142.00
Purchase #5	$18.68	7.817%	$20.1402	$20.14	$20.15	$20.10
Purchase #6	$128.74	5.834%	$136.2507	$136.25	$136.25	$136.30
Purchase #7	$64.52	11.478%	$71.9256	$71.93	$71.95	$71.90
7 purchase totals =	$1,019.07		$1,100.5148	$1,100.52	$1,100.50	$1,100.50