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	$188.56	9.230%	$205.9641	$205.96	$205.95	$206.00
Purchase #2	$103.26	6.356%	$109.8232	$109.82	$109.80	$109.80
Purchase #3	$55.38	8.188%	$59.9145	$59.91	$59.90	$59.90
Purchase #4	$150.82	12.592%	$169.8113	$169.81	$169.80	$169.80
Purchase #5	$158.85	12.253%	$178.3139	$178.31	$178.30	$178.30
Purchase #6	$88.94	13.618%	$101.0518	$101.05	$101.05	$101.10
Purchase #7	$79.92	10.229%	$88.095	$88.10	$88.10	$88.10
7 purchase totals =	$825.73		$912.9738	$912.96	$912.90	$913.00