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	$225.54	12.852%	$254.5264	$254.53	$254.55	$254.50
Purchase #2	$134.76	13.411%	$152.8327	$152.83	$152.85	$152.80
Purchase #3	$216.74	7.549%	$233.1017	$233.10	$233.10	$233.10
Purchase #4	$182.58	7.565%	$196.3922	$196.39	$196.40	$196.40
Purchase #5	$5.32	13.662%	$6.0468	$6.05	$6.05	$6.00
Purchase #6	$28.86	7.476%	$31.0176	$31.02	$31.00	$31.00
Purchase #7	$190.29	7.280%	$204.1431	$204.14	$204.15	$204.10
7 purchase totals =	$984.09		$1,078.0605	$1,078.06	$1,078.10	$1,077.90