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	$27.93	3.180%	$28.8182	$28.82	$28.80	$28.80
Purchase #2	$42.64	10.854%	$47.2681	$47.27	$47.25	$47.30
Purchase #3	$118.71	10.769%	$131.4939	$131.49	$131.50	$131.50
Purchase #4	$35.46	9.552%	$38.8471	$38.85	$38.85	$38.80
Purchase #5	$135.53	6.786%	$144.7271	$144.73	$144.75	$144.70
Purchase #6	$72.30	13.495%	$82.0569	$82.06	$82.05	$82.10
Purchase #7	$198.64	5.135%	$208.8402	$208.84	$208.85	$208.80
7 purchase totals =	$631.21		$682.0515	$682.06	$682.05	$682.00