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	$153.88	10.774%	$170.459	$170.46	$170.45	$170.50
Purchase #2	$151.37	11.434%	$168.6776	$168.68	$168.70	$168.70
Purchase #3	$184.33	7.713%	$198.5474	$198.55	$198.55	$198.50
Purchase #4	$134.83	5.864%	$142.7364	$142.74	$142.75	$142.70
Purchase #5	$56.85	5.440%	$59.9426	$59.94	$59.95	$59.90
Purchase #6	$184.79	13.393%	$209.5389	$209.54	$209.55	$209.50
Purchase #7	$193.34	8.600%	$209.9672	$209.97	$209.95	$210.00
7 purchase totals =	$1,059.39		$1,159.8691	$1,159.88	$1,159.90	$1,159.80