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	$206.73	11.565%	$230.6383	$230.64	$230.65	$230.60
Purchase #2	$84.44	6.347%	$89.7994	$89.80	$89.80	$89.80
Purchase #3	$101.46	3.818%	$105.3337	$105.33	$105.35	$105.30
Purchase #4	$27.33	4.543%	$28.5716	$28.57	$28.55	$28.60
Purchase #5	$88.27	9.413%	$96.5789	$96.58	$96.60	$96.60
Purchase #6	$219.61	5.254%	$231.1483	$231.15	$231.15	$231.10
Purchase #7	$229.81	7.196%	$246.3471	$246.35	$246.35	$246.30
7 purchase totals =	$957.65		$1,028.4173	$1,028.42	$1,028.45	$1,028.30