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	$78.57	5.812%	$83.1365	$83.14	$83.15	$83.10
Purchase #2	$198.96	13.426%	$225.6724	$225.67	$225.65	$225.70
Purchase #3	$218.39	12.392%	$245.4529	$245.45	$245.45	$245.50
Purchase #4	$119.48	9.751%	$131.1305	$131.13	$131.15	$131.10
Purchase #5	$79.48	10.326%	$87.6871	$87.69	$87.70	$87.70
Purchase #6	$164.67	4.105%	$171.4297	$171.43	$171.45	$171.40
Purchase #7	$72.42	4.673%	$75.8042	$75.80	$75.80	$75.80
7 purchase totals =	$931.97		$1,020.3133	$1,020.31	$1,020.35	$1,020.30