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	$172.91	9.621%	$189.5457	$189.55	$189.55	$189.50
Purchase #2	$151.48	13.631%	$172.1282	$172.13	$172.15	$172.10
Purchase #3	$98.67	10.729%	$109.2563	$109.26	$109.25	$109.30
Purchase #4	$24.30	12.592%	$27.3599	$27.36	$27.35	$27.40
Purchase #5	$94.32	11.634%	$105.2932	$105.29	$105.30	$105.30
Purchase #6	$21.34	13.406%	$24.2008	$24.20	$24.20	$24.20
Purchase #7	$84.53	13.706%	$96.1157	$96.12	$96.10	$96.10
7 purchase totals =	$647.55		$723.8998	$723.91	$723.90	$723.90