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	$183.69	9.365%	$200.8926	$200.89	$200.90	$200.90
Purchase #2	$96.50	13.139%	$109.1791	$109.18	$109.20	$109.20
Purchase #3	$64.72	9.265%	$70.7163	$70.72	$70.70	$70.70
Purchase #4	$55.73	11.752%	$62.2794	$62.28	$62.30	$62.30
Purchase #5	$82.56	4.569%	$86.3322	$86.33	$86.35	$86.30
Purchase #6	$155.70	10.279%	$171.7044	$171.70	$171.70	$171.70
Purchase #7	$220.48	8.212%	$238.5858	$238.59	$238.60	$238.60
7 purchase totals =	$859.38		$939.6898	$939.69	$939.75	$939.70