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	$94.43	6.411%	$100.4839	$100.48	$100.50	$100.50
Purchase #2	$102.75	11.343%	$114.4049	$114.40	$114.40	$114.40
Purchase #3	$12.44	6.392%	$13.2352	$13.24	$13.25	$13.20
Purchase #4	$93.70	11.666%	$104.631	$104.63	$104.65	$104.60
Purchase #5	$78.78	3.426%	$81.479	$81.48	$81.50	$81.50
Purchase #6	$84.47	8.109%	$91.3197	$91.32	$91.30	$91.30
Purchase #7	$47.50	7.269%	$50.9528	$50.95	$50.95	$51.00
7 purchase totals =	$514.07		$556.5065	$556.50	$556.55	$556.50