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	$249.91	3.481%	$258.6094	$258.61	$258.60	$258.60
Purchase #2	$184.76	6.571%	$196.9006	$196.90	$196.90	$196.90
Purchase #3	$80.82	11.221%	$89.8888	$89.89	$89.90	$89.90
Purchase #4	$119.44	4.614%	$124.951	$124.95	$124.95	$125.00
Purchase #5	$223.30	3.561%	$231.2517	$231.25	$231.25	$231.30
Purchase #6	$123.74	11.482%	$137.9478	$137.95	$137.95	$137.90
Purchase #7	$90.61	13.225%	$102.5932	$102.59	$102.60	$102.60
7 purchase totals =	$1,072.58		$1,142.1425	$1,142.14	$1,142.15	$1,142.20