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	$19.30	12.724%	$21.7557	$21.76	$21.75	$21.80
Purchase #2	$23.46	10.291%	$25.8743	$25.87	$25.85	$25.90
Purchase #3	$232.81	9.272%	$254.3961	$254.40	$254.40	$254.40
Purchase #4	$119.52	3.572%	$123.7893	$123.79	$123.80	$123.80
Purchase #5	$106.99	3.574%	$110.8138	$110.81	$110.80	$110.80
Purchase #6	$86.69	3.439%	$89.6713	$89.67	$89.65	$89.70
Purchase #7	$109.59	12.269%	$123.0356	$123.04	$123.05	$123.00
7 purchase totals =	$698.36		$749.3361	$749.34	$749.30	$749.40