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	$17.48	8.224%	$18.9176	$18.92	$18.90	$18.90
Purchase #2	$86.57	5.447%	$91.2855	$91.29	$91.30	$91.30
Purchase #3	$70.46	11.688%	$78.6954	$78.70	$78.70	$78.70
Purchase #4	$236.87	11.805%	$264.8325	$264.83	$264.85	$264.80
Purchase #5	$187.35	5.129%	$196.9592	$196.96	$196.95	$197.00
Purchase #6	$208.40	9.406%	$228.0021	$228.00	$228.00	$228.00
Purchase #7	$173.57	9.111%	$189.384	$189.38	$189.40	$189.40
7 purchase totals =	$980.70		$1,068.0763	$1,068.08	$1,068.10	$1,068.10