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	$94.49	5.869%	$100.0356	$100.04	$100.05	$100.00
Purchase #2	$72.47	6.705%	$77.3291	$77.33	$77.35	$77.30
Purchase #3	$112.37	9.634%	$123.1957	$123.20	$123.20	$123.20
Purchase #4	$174.43	6.304%	$185.4261	$185.43	$185.45	$185.40
Purchase #5	$147.83	5.669%	$156.2105	$156.21	$156.20	$156.20
Purchase #6	$141.55	10.364%	$156.2202	$156.22	$156.20	$156.20
Purchase #7	$79.53	12.303%	$89.3146	$89.31	$89.30	$89.30
7 purchase totals =	$822.67		$887.7318	$887.74	$887.75	$887.60