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	$27.89	3.432%	$28.8472	$28.85	$28.85	$28.80
Purchase #2	$182.67	9.821%	$200.61	$200.61	$200.60	$200.60
Purchase #3	$236.87	9.181%	$258.617	$258.62	$258.60	$258.60
Purchase #4	$95.35	5.633%	$100.7211	$100.72	$100.70	$100.70
Purchase #5	$6.94	6.345%	$7.3803	$7.38	$7.40	$7.40
Purchase #6	$92.66	11.491%	$103.3076	$103.31	$103.30	$103.30
Purchase #7	$69.41	7.270%	$74.4561	$74.46	$74.45	$74.50
7 purchase totals =	$711.79		$773.9393	$773.95	$773.90	$773.90