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	$46.76	13.792%	$53.2091	$53.21	$53.20	$53.20
Purchase #2	$247.93	11.802%	$277.1907	$277.19	$277.20	$277.20
Purchase #3	$30.80	3.537%	$31.8894	$31.89	$31.90	$31.90
Purchase #4	$212.88	3.557%	$220.4521	$220.45	$220.45	$220.50
Purchase #5	$108.59	13.391%	$123.1313	$123.13	$123.15	$123.10
Purchase #6	$185.26	6.247%	$196.8332	$196.83	$196.85	$196.80
Purchase #7	$170.44	10.113%	$187.6766	$187.68	$187.70	$187.70
7 purchase totals =	$1,002.66		$1,090.3824	$1,090.38	$1,090.45	$1,090.40