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	$240.38	5.622%	$253.8942	$253.89	$253.90	$253.90
Purchase #2	$166.25	12.127%	$186.4111	$186.41	$186.40	$186.40
Purchase #3	$191.59	9.840%	$210.4425	$210.44	$210.45	$210.40
Purchase #4	$85.78	12.363%	$96.385	$96.39	$96.40	$96.40
Purchase #5	$169.58	9.189%	$185.1627	$185.16	$185.15	$185.20
Purchase #6	$65.74	6.262%	$69.8566	$69.86	$69.85	$69.90
Purchase #7	$91.35	7.870%	$98.5392	$98.54	$98.55	$98.50
7 purchase totals =	$1,010.67		$1,100.6913	$1,100.69	$1,100.70	$1,100.70