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	$48.97	3.227%	$50.5503	$50.55	$50.55	$50.60
Purchase #2	$184.59	3.761%	$191.5324	$191.53	$191.55	$191.50
Purchase #3	$138.87	4.794%	$145.5274	$145.53	$145.55	$145.50
Purchase #4	$157.81	12.294%	$177.2112	$177.21	$177.20	$177.20
Purchase #5	$240.27	6.268%	$255.3301	$255.33	$255.35	$255.30
Purchase #6	$79.56	12.475%	$89.4851	$89.49	$89.50	$89.50
Purchase #7	$234.46	4.535%	$245.0928	$245.09	$245.10	$245.10
7 purchase totals =	$1,084.53		$1,154.7293	$1,154.73	$1,154.80	$1,154.70