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	$218.69	8.107%	$236.4192	$236.42	$236.40	$236.40
Purchase #2	$67.54	6.647%	$72.0294	$72.03	$72.05	$72.00
Purchase #3	$74.77	7.194%	$80.149	$80.15	$80.15	$80.10
Purchase #4	$166.34	8.769%	$180.9264	$180.93	$180.95	$180.90
Purchase #5	$38.74	3.546%	$40.1137	$40.11	$40.10	$40.10
Purchase #6	$237.96	5.417%	$250.8503	$250.85	$250.85	$250.90
Purchase #7	$36.60	9.421%	$40.0481	$40.05	$40.05	$40.00
7 purchase totals =	$840.64		$900.5361	$900.54	$900.55	$900.40