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	$37.36	9.471%	$40.8984	$40.90	$40.90	$40.90
Purchase #2	$144.31	8.653%	$156.7971	$156.80	$156.80	$156.80
Purchase #3	$237.46	13.554%	$269.6453	$269.65	$269.65	$269.60
Purchase #4	$245.26	8.613%	$266.3842	$266.38	$266.40	$266.40
Purchase #5	$75.63	11.721%	$84.4946	$84.49	$84.50	$84.50
Purchase #6	$38.61	8.331%	$41.8266	$41.83	$41.85	$41.80
Purchase #7	$72.41	13.264%	$82.0145	$82.01	$82.00	$82.00
7 purchase totals =	$851.04		$942.0607	$942.06	$942.10	$942.00