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	$123.26	11.632%	$137.5976	$137.60	$137.60	$137.60
Purchase #2	$192.30	9.816%	$211.1762	$211.18	$211.20	$211.20
Purchase #3	$90.48	3.744%	$93.8676	$93.87	$93.85	$93.90
Purchase #4	$123.57	9.176%	$134.9088	$134.91	$134.90	$134.90
Purchase #5	$179.50	10.612%	$198.5485	$198.55	$198.55	$198.50
Purchase #6	$39.89	10.669%	$44.1459	$44.15	$44.15	$44.10
Purchase #7	$199.51	11.338%	$222.1304	$222.13	$222.15	$222.10
7 purchase totals =	$948.51		$1,042.3750	$1,042.39	$1,042.40	$1,042.30