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	$203.84	3.404%	$210.7787	$210.78	$210.80	$210.80
Purchase #2	$196.66	12.142%	$220.5385	$220.54	$220.55	$220.50
Purchase #3	$96.25	6.179%	$102.1973	$102.20	$102.20	$102.20
Purchase #4	$250.79	5.713%	$265.1176	$265.12	$265.10	$265.10
Purchase #5	$80.51	11.350%	$89.6479	$89.65	$89.65	$89.60
Purchase #6	$37.61	4.491%	$39.2991	$39.30	$39.30	$39.30
Purchase #7	$92.78	7.804%	$100.0206	$100.02	$100.00	$100.00
7 purchase totals =	$958.44		$1,027.5997	$1,027.61	$1,027.60	$1,027.50