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	$150.82	5.120%	$158.542	$158.54	$158.55	$158.50
Purchase #2	$236.53	11.566%	$263.8871	$263.89	$263.90	$263.90
Purchase #3	$80.54	11.368%	$89.6958	$89.70	$89.70	$89.70
Purchase #4	$96.74	8.347%	$104.8149	$104.81	$104.80	$104.80
Purchase #5	$135.85	4.867%	$142.4618	$142.46	$142.45	$142.50
Purchase #6	$71.91	9.308%	$78.6034	$78.60	$78.60	$78.60
Purchase #7	$33.81	6.864%	$36.1307	$36.13	$36.15	$36.10
7 purchase totals =	$806.20		$874.1357	$874.13	$874.15	$874.10