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	$177.70	4.335%	$185.4033	$185.40	$185.40	$185.40
Purchase #2	$40.87	4.772%	$42.8203	$42.82	$42.80	$42.80
Purchase #3	$101.71	10.140%	$112.0234	$112.02	$112.00	$112.00
Purchase #4	$64.48	11.475%	$71.8791	$71.88	$71.90	$71.90
Purchase #5	$90.65	6.774%	$96.7906	$96.79	$96.80	$96.80
Purchase #6	$37.93	11.396%	$42.2525	$42.25	$42.25	$42.30
Purchase #7	$99.75	12.558%	$112.2766	$112.28	$112.30	$112.30
7 purchase totals =	$613.09		$663.4458	$663.44	$663.45	$663.50