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	$151.64	6.507%	$161.5072	$161.51	$161.50	$161.50
Purchase #2	$83.44	3.394%	$86.272	$86.27	$86.25	$86.30
Purchase #3	$86.76	3.729%	$89.9953	$90.00	$90.00	$90.00
Purchase #4	$102.41	6.747%	$109.3196	$109.32	$109.30	$109.30
Purchase #5	$206.64	11.453%	$230.3065	$230.31	$230.30	$230.30
Purchase #6	$81.62	8.789%	$88.7936	$88.79	$88.80	$88.80
Purchase #7	$81.68	9.199%	$89.1937	$89.19	$89.20	$89.20
7 purchase totals =	$794.19		$855.3879	$855.39	$855.35	$855.40