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	$90.78	11.138%	$100.8911	$100.89	$100.90	$100.90
Purchase #2	$47.28	12.761%	$53.3134	$53.31	$53.30	$53.30
Purchase #3	$244.45	7.408%	$262.5589	$262.56	$262.55	$262.60
Purchase #4	$130.47	4.405%	$136.2172	$136.22	$136.20	$136.20
Purchase #5	$82.91	4.309%	$86.4826	$86.48	$86.50	$86.50
Purchase #6	$125.60	12.847%	$141.7358	$141.74	$141.75	$141.70
Purchase #7	$64.50	3.579%	$66.8085	$66.81	$66.80	$66.80
7 purchase totals =	$785.99		$848.0075	$848.01	$848.00	$848.00