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	$93.33	11.167%	$103.7522	$103.75	$103.75	$103.80
Purchase #2	$237.74	10.418%	$262.5078	$262.51	$262.50	$262.50
Purchase #3	$180.50	4.433%	$188.5016	$188.50	$188.50	$188.50
Purchase #4	$52.86	4.732%	$55.3613	$55.36	$55.35	$55.40
Purchase #5	$155.87	13.159%	$176.3809	$176.38	$176.40	$176.40
Purchase #6	$60.42	11.726%	$67.5048	$67.50	$67.50	$67.50
Purchase #7	$212.25	4.677%	$222.1769	$222.18	$222.20	$222.20
7 purchase totals =	$992.97		$1,076.1855	$1,076.18	$1,076.20	$1,076.30