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	$76.84	4.311%	$80.1526	$80.15	$80.15	$80.20
Purchase #2	$156.84	7.367%	$168.3944	$168.39	$168.40	$168.40
Purchase #3	$53.29	6.696%	$56.8583	$56.86	$56.85	$56.90
Purchase #4	$7.33	6.386%	$7.7981	$7.80	$7.80	$7.80
Purchase #5	$47.37	8.816%	$51.5461	$51.55	$51.55	$51.50
Purchase #6	$192.96	13.430%	$218.8745	$218.87	$218.85	$218.90
Purchase #7	$40.95	11.855%	$45.8046	$45.80	$45.80	$45.80
7 purchase totals =	$575.58		$629.4286	$629.42	$629.40	$629.50