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	$154.50	6.649%	$164.7727	$164.77	$164.75	$164.80
Purchase #2	$33.57	11.345%	$37.3785	$37.38	$37.40	$37.40
Purchase #3	$215.66	13.873%	$245.5785	$245.58	$245.60	$245.60
Purchase #4	$68.56	12.488%	$77.1218	$77.12	$77.10	$77.10
Purchase #5	$171.46	8.207%	$185.5317	$185.53	$185.55	$185.50
Purchase #6	$62.92	6.761%	$67.174	$67.17	$67.15	$67.20
Purchase #7	$164.96	9.474%	$180.5883	$180.59	$180.60	$180.60
7 purchase totals =	$871.63		$958.1455	$958.14	$958.15	$958.20