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	$249.33	3.646%	$258.4206	$258.42	$258.40	$258.40
Purchase #2	$189.30	5.187%	$199.119	$199.12	$199.10	$199.10
Purchase #3	$229.32	5.491%	$241.912	$241.91	$241.90	$241.90
Purchase #4	$78.48	9.152%	$85.6625	$85.66	$85.65	$85.70
Purchase #5	$109.82	6.526%	$116.9869	$116.99	$117.00	$117.00
Purchase #6	$90.86	5.712%	$96.0499	$96.05	$96.05	$96.00
Purchase #7	$127.48	13.588%	$144.802	$144.80	$144.80	$144.80
7 purchase totals =	$1,074.59		$1,142.9529	$1,142.95	$1,142.90	$1,142.90