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	$232.86	4.733%	$243.8813	$243.88	$243.90	$243.90
Purchase #2	$59.99	3.220%	$61.9217	$61.92	$61.90	$61.90
Purchase #3	$194.50	7.762%	$209.5971	$209.60	$209.60	$209.60
Purchase #4	$39.82	4.463%	$41.5972	$41.60	$41.60	$41.60
Purchase #5	$113.54	6.462%	$120.877	$120.88	$120.90	$120.90
Purchase #6	$104.39	3.682%	$108.2336	$108.23	$108.25	$108.20
Purchase #7	$165.63	3.660%	$171.6921	$171.69	$171.70	$171.70
7 purchase totals =	$910.73		$957.8000	$957.80	$957.85	$957.80