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	$33.41	13.599%	$37.9534	$37.95	$37.95	$38.00
Purchase #2	$104.65	5.570%	$110.479	$110.48	$110.50	$110.50
Purchase #3	$13.76	13.336%	$15.595	$15.60	$15.60	$15.60
Purchase #4	$76.86	6.724%	$82.0281	$82.03	$82.05	$82.00
Purchase #5	$133.37	6.757%	$142.3818	$142.38	$142.40	$142.40
Purchase #6	$242.53	9.374%	$265.2648	$265.26	$265.25	$265.30
Purchase #7	$179.57	11.675%	$200.5348	$200.53	$200.55	$200.50
7 purchase totals =	$784.15		$854.2369	$854.23	$854.30	$854.30