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	$178.92	4.282%	$186.5814	$186.58	$186.60	$186.60
Purchase #2	$147.75	11.151%	$164.2256	$164.23	$164.25	$164.20
Purchase #3	$219.38	6.351%	$233.3128	$233.31	$233.30	$233.30
Purchase #4	$157.80	6.124%	$167.4637	$167.46	$167.45	$167.50
Purchase #5	$80.73	8.302%	$87.4322	$87.43	$87.45	$87.40
Purchase #6	$200.56	7.397%	$215.3954	$215.40	$215.40	$215.40
Purchase #7	$127.68	7.532%	$137.2969	$137.30	$137.30	$137.30
7 purchase totals =	$1,112.82		$1,191.7080	$1,191.71	$1,191.75	$1,191.70