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	$107.57	9.530%	$117.8214	$117.82	$117.80	$117.80
Purchase #2	$228.94	10.391%	$252.7292	$252.73	$252.75	$252.70
Purchase #3	$140.28	8.735%	$152.5335	$152.53	$152.55	$152.50
Purchase #4	$73.64	7.216%	$78.9539	$78.95	$78.95	$79.00
Purchase #5	$91.92	7.753%	$99.0466	$99.05	$99.05	$99.00
Purchase #6	$170.25	12.460%	$191.4632	$191.46	$191.45	$191.50
Purchase #7	$20.97	4.386%	$21.8897	$21.89	$21.90	$21.90
7 purchase totals =	$833.57		$914.4375	$914.43	$914.45	$914.40