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	$208.32	8.181%	$225.3627	$225.36	$225.35	$225.40
Purchase #2	$124.29	12.638%	$139.9978	$140.00	$140.00	$140.00
Purchase #3	$62.76	12.135%	$70.3759	$70.38	$70.40	$70.40
Purchase #4	$75.32	6.571%	$80.2693	$80.27	$80.25	$80.30
Purchase #5	$161.34	4.190%	$168.1001	$168.10	$168.10	$168.10
Purchase #6	$54.69	9.404%	$59.833	$59.83	$59.85	$59.80
Purchase #7	$147.68	12.486%	$166.1193	$166.12	$166.10	$166.10
7 purchase totals =	$834.40		$910.0581	$910.06	$910.05	$910.10