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	$137.72	3.253%	$142.2	$142.20	$142.20	$142.20
Purchase #2	$64.51	12.592%	$72.6331	$72.63	$72.65	$72.60
Purchase #3	$167.37	11.742%	$187.0226	$187.02	$187.00	$187.00
Purchase #4	$47.80	6.802%	$51.0514	$51.05	$51.05	$51.10
Purchase #5	$40.50	7.235%	$43.4302	$43.43	$43.45	$43.40
Purchase #6	$88.98	13.333%	$100.8437	$100.84	$100.85	$100.80
Purchase #7	$231.29	7.175%	$247.8851	$247.89	$247.90	$247.90
7 purchase totals =	$778.17		$845.0661	$845.06	$845.10	$845.00