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	$203.73	12.646%	$229.4937	$229.49	$229.50	$229.50
Purchase #2	$177.56	7.734%	$191.2925	$191.29	$191.30	$191.30
Purchase #3	$82.32	11.289%	$91.6131	$91.61	$91.60	$91.60
Purchase #4	$228.62	4.305%	$238.4621	$238.46	$238.45	$238.50
Purchase #5	$84.29	8.564%	$91.5086	$91.51	$91.50	$91.50
Purchase #6	$90.31	10.809%	$100.0716	$100.07	$100.05	$100.10
Purchase #7	$19.71	7.739%	$21.2354	$21.24	$21.25	$21.20
7 purchase totals =	$886.54		$963.6770	$963.67	$963.65	$963.70