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	$55.64	3.161%	$57.3988	$57.40	$57.40	$57.40
Purchase #2	$147.29	6.165%	$156.3704	$156.37	$156.35	$156.40
Purchase #3	$189.83	3.251%	$196.0014	$196.00	$196.00	$196.00
Purchase #4	$92.81	11.697%	$103.666	$103.67	$103.65	$103.70
Purchase #5	$213.73	9.214%	$233.4231	$233.42	$233.40	$233.40
Purchase #6	$140.61	7.583%	$151.2725	$151.27	$151.25	$151.30
Purchase #7	$202.71	13.480%	$230.0353	$230.04	$230.05	$230.00
7 purchase totals =	$1,042.62		$1,128.1675	$1,128.17	$1,128.10	$1,128.20