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	$123.84	10.411%	$136.733	$136.73	$136.75	$136.70
Purchase #2	$236.36	11.481%	$263.4965	$263.50	$263.50	$263.50
Purchase #3	$19.55	7.610%	$21.0378	$21.04	$21.05	$21.00
Purchase #4	$112.56	6.217%	$119.5579	$119.56	$119.55	$119.60
Purchase #5	$23.61	5.550%	$24.9204	$24.92	$24.90	$24.90
Purchase #6	$174.30	11.705%	$194.7018	$194.70	$194.70	$194.70
Purchase #7	$79.39	12.642%	$89.4265	$89.43	$89.45	$89.40
7 purchase totals =	$769.61		$849.8739	$849.88	$849.90	$849.80