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	$65.89	6.811%	$70.3778	$70.38	$70.40	$70.40
Purchase #2	$204.90	4.105%	$213.3111	$213.31	$213.30	$213.30
Purchase #3	$242.71	5.740%	$256.6416	$256.64	$256.65	$256.60
Purchase #4	$162.39	4.568%	$169.808	$169.81	$169.80	$169.80
Purchase #5	$179.88	5.550%	$189.8633	$189.86	$189.85	$189.90
Purchase #6	$150.80	11.291%	$167.8268	$167.83	$167.85	$167.80
Purchase #7	$108.39	9.621%	$118.8182	$118.82	$118.80	$118.80
7 purchase totals =	$1,114.96		$1,186.6468	$1,186.65	$1,186.65	$1,186.60