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	$228.43	5.218%	$240.3495	$240.35	$240.35	$240.30
Purchase #2	$150.86	11.501%	$168.2104	$168.21	$168.20	$168.20
Purchase #3	$17.82	9.655%	$19.5405	$19.54	$19.55	$19.50
Purchase #4	$157.68	9.817%	$173.1594	$173.16	$173.15	$173.20
Purchase #5	$133.48	4.507%	$139.4959	$139.50	$139.50	$139.50
Purchase #6	$67.50	3.816%	$70.0758	$70.08	$70.10	$70.10
Purchase #7	$81.35	5.789%	$86.0594	$86.06	$86.05	$86.10
7 purchase totals =	$837.12		$896.8909	$896.90	$896.90	$896.90