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	$29.87	13.135%	$33.7934	$33.79	$33.80	$33.80
Purchase #2	$57.86	3.357%	$59.8024	$59.80	$59.80	$59.80
Purchase #3	$60.55	5.860%	$64.0982	$64.10	$64.10	$64.10
Purchase #4	$98.74	11.251%	$109.8492	$109.85	$109.85	$109.80
Purchase #5	$62.46	3.317%	$64.5318	$64.53	$64.55	$64.50
Purchase #6	$141.52	9.757%	$155.3281	$155.33	$155.35	$155.30
Purchase #7	$63.61	13.448%	$72.1643	$72.16	$72.15	$72.20
7 purchase totals =	$514.61		$559.5674	$559.56	$559.60	$559.50