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	$47.75	11.139%	$53.0689	$53.07	$53.05	$53.10
Purchase #2	$136.74	8.467%	$148.3178	$148.32	$148.30	$148.30
Purchase #3	$125.36	11.567%	$139.8604	$139.86	$139.85	$139.90
Purchase #4	$102.56	13.609%	$116.5174	$116.52	$116.50	$116.50
Purchase #5	$156.59	7.778%	$168.7696	$168.77	$168.75	$168.80
Purchase #6	$246.77	5.813%	$261.1147	$261.11	$261.10	$261.10
Purchase #7	$105.73	5.148%	$111.173	$111.17	$111.15	$111.20
7 purchase totals =	$921.50		$998.8218	$998.82	$998.70	$998.90