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	$77.47	4.555%	$80.9988	$81.00	$81.00	$81.00
Purchase #2	$168.26	11.471%	$187.5611	$187.56	$187.55	$187.60
Purchase #3	$155.31	10.614%	$171.7946	$171.79	$171.80	$171.80
Purchase #4	$248.54	12.809%	$280.3755	$280.38	$280.40	$280.40
Purchase #5	$77.80	10.412%	$85.9005	$85.90	$85.90	$85.90
Purchase #6	$14.97	4.810%	$15.6901	$15.69	$15.70	$15.70
Purchase #7	$105.80	13.224%	$119.791	$119.79	$119.80	$119.80
7 purchase totals =	$848.15		$942.1116	$942.11	$942.15	$942.20