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	$170.57	10.280%	$188.1046	$188.10	$188.10	$188.10
Purchase #2	$40.49	10.708%	$44.8257	$44.83	$44.85	$44.80
Purchase #3	$136.82	8.674%	$148.6878	$148.69	$148.70	$148.70
Purchase #4	$238.41	10.568%	$263.6052	$263.61	$263.60	$263.60
Purchase #5	$101.67	9.200%	$111.0236	$111.02	$111.00	$111.00
Purchase #6	$54.34	6.690%	$57.9753	$57.98	$58.00	$58.00
Purchase #7	$153.31	9.654%	$168.1105	$168.11	$168.10	$168.10
7 purchase totals =	$895.61		$982.3327	$982.34	$982.35	$982.30