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	$72.59	10.356%	$80.1074	$80.11	$80.10	$80.10
Purchase #2	$83.37	12.418%	$93.7229	$93.72	$93.70	$93.70
Purchase #3	$13.45	10.486%	$14.8604	$14.86	$14.85	$14.90
Purchase #4	$38.82	7.861%	$41.8716	$41.87	$41.85	$41.90
Purchase #5	$98.81	13.420%	$112.0703	$112.07	$112.05	$112.10
Purchase #6	$6.74	6.113%	$7.152	$7.15	$7.15	$7.20
Purchase #7	$41.62	4.620%	$43.5428	$43.54	$43.55	$43.50
7 purchase totals =	$355.40		$393.3274	$393.32	$393.25	$393.40