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	$56.88	12.774%	$64.1459	$64.15	$64.15	$64.10
Purchase #2	$160.56	8.686%	$174.5062	$174.51	$174.50	$174.50
Purchase #3	$162.46	13.551%	$184.475	$184.48	$184.50	$184.50
Purchase #4	$166.59	5.418%	$175.6158	$175.62	$175.60	$175.60
Purchase #5	$113.25	7.515%	$121.7607	$121.76	$121.75	$121.80
Purchase #6	$80.53	11.696%	$89.9488	$89.95	$89.95	$89.90
Purchase #7	$107.71	3.800%	$111.803	$111.80	$111.80	$111.80
7 purchase totals =	$847.98		$922.2554	$922.27	$922.25	$922.20