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	$210.43	6.609%	$224.3373	$224.34	$224.35	$224.30
Purchase #2	$120.72	6.515%	$128.5849	$128.58	$128.60	$128.60
Purchase #3	$85.87	3.105%	$88.5363	$88.54	$88.55	$88.50
Purchase #4	$154.91	6.871%	$165.5539	$165.55	$165.55	$165.60
Purchase #5	$158.30	4.557%	$165.5137	$165.51	$165.50	$165.50
Purchase #6	$83.46	8.780%	$90.7878	$90.79	$90.80	$90.80
Purchase #7	$54.96	7.745%	$59.2167	$59.22	$59.20	$59.20
7 purchase totals =	$868.65		$922.5306	$922.53	$922.55	$922.50