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	$240.27	4.216%	$250.3998	$250.40	$250.40	$250.40
Purchase #2	$200.35	10.113%	$220.6114	$220.61	$220.60	$220.60
Purchase #3	$183.59	12.827%	$207.1391	$207.14	$207.15	$207.10
Purchase #4	$88.77	4.622%	$92.8729	$92.87	$92.85	$92.90
Purchase #5	$119.57	3.145%	$123.3305	$123.33	$123.35	$123.30
Purchase #6	$59.72	7.550%	$64.2289	$64.23	$64.25	$64.20
Purchase #7	$57.34	9.797%	$62.9576	$62.96	$62.95	$63.00
7 purchase totals =	$949.61		$1,021.5402	$1,021.54	$1,021.55	$1,021.50