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	$90.49	9.841%	$99.3951	$99.40	$99.40	$99.40
Purchase #2	$123.46	6.506%	$131.4923	$131.49	$131.50	$131.50
Purchase #3	$139.26	9.381%	$152.324	$152.32	$152.30	$152.30
Purchase #4	$133.88	13.691%	$152.2095	$152.21	$152.20	$152.20
Purchase #5	$37.31	3.506%	$38.6181	$38.62	$38.60	$38.60
Purchase #6	$89.42	13.685%	$101.6571	$101.66	$101.65	$101.70
Purchase #7	$73.52	8.605%	$79.8464	$79.85	$79.85	$79.80
7 purchase totals =	$687.34		$755.5425	$755.55	$755.50	$755.50