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	$245.87	12.579%	$276.798	$276.80	$276.80	$276.80
Purchase #2	$116.33	6.354%	$123.7216	$123.72	$123.70	$123.70
Purchase #3	$169.78	10.334%	$187.3251	$187.33	$187.35	$187.30
Purchase #4	$156.73	11.829%	$175.2696	$175.27	$175.25	$175.30
Purchase #5	$123.70	12.846%	$139.5905	$139.59	$139.60	$139.60
Purchase #6	$118.69	6.249%	$126.1069	$126.11	$126.10	$126.10
Purchase #7	$50.34	11.123%	$55.9393	$55.94	$55.95	$55.90
7 purchase totals =	$981.44		$1,084.7510	$1,084.76	$1,084.75	$1,084.70