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	$37.90	13.579%	$43.0464	$43.05	$43.05	$43.00
Purchase #2	$184.52	6.499%	$196.512	$196.51	$196.50	$196.50
Purchase #3	$42.46	11.597%	$47.3841	$47.38	$47.40	$47.40
Purchase #4	$84.88	13.284%	$96.1555	$96.16	$96.15	$96.20
Purchase #5	$46.99	9.191%	$51.3089	$51.31	$51.30	$51.30
Purchase #6	$76.89	4.785%	$80.5692	$80.57	$80.55	$80.60
Purchase #7	$76.94	13.758%	$87.5254	$87.53	$87.55	$87.50
7 purchase totals =	$550.58		$602.5015	$602.51	$602.50	$602.50