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	$210.89	6.393%	$224.3722	$224.37	$224.35	$224.40
Purchase #2	$53.54	6.721%	$57.1384	$57.14	$57.15	$57.10
Purchase #3	$241.54	4.815%	$253.1702	$253.17	$253.15	$253.20
Purchase #4	$170.89	10.821%	$189.382	$189.38	$189.40	$189.40
Purchase #5	$189.59	13.296%	$214.7979	$214.80	$214.80	$214.80
Purchase #6	$38.55	8.483%	$41.8202	$41.82	$41.80	$41.80
Purchase #7	$135.33	11.145%	$150.4125	$150.41	$150.40	$150.40
7 purchase totals =	$1,040.33		$1,131.0934	$1,131.09	$1,131.05	$1,131.10