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	$165.90	10.425%	$183.1951	$183.20	$183.20	$183.20
Purchase #2	$174.67	6.455%	$185.9449	$185.94	$185.95	$185.90
Purchase #3	$53.61	11.317%	$59.677	$59.68	$59.70	$59.70
Purchase #4	$178.30	4.520%	$186.3592	$186.36	$186.35	$186.40
Purchase #5	$84.42	6.131%	$89.5958	$89.60	$89.60	$89.60
Purchase #6	$65.63	9.838%	$72.0867	$72.09	$72.10	$72.10
Purchase #7	$53.71	12.560%	$60.456	$60.46	$60.45	$60.50
7 purchase totals =	$776.24		$837.3147	$837.33	$837.35	$837.40